InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
Define concurrent lines |
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Answer» Three lines are said to be concurrent, if they pass through a common point.i.e., three lines are said to be concurrent if the point of intersection of two of them lies on the third line. |
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| 52. |
Write the coordinates of the orthocenter of the triangle formed by the lines xy = 0 and x + y = 1 |
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Answer» Given: Lines xy = 0 and x + y = 1 To find: The coordinates of the orthocenter of the triangle formed by the lines xy = 0 and x + y = 1 Explanation: The equation xy = 0 represents a pair of straight lines. The lines can be written separately in the following way: x = 0 … (1) y = 0 … (2) The third line is x + y = 1 … (3) Lines (1) and (2) are perpendicular to each other as they are coordinate axes. Therefore, the triangle formed by the lines (1), (2) and (3) is a right-angled triangle. Thus, the or the centre of the triangle formed by the given lines is the intersection of x = 0 and y = 0, which is (0, 0). |
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| 53. |
The inclination of the line x – y + 3 = 0 with the positive direction of x-axis is(A) 45° (B) 135° (C) – 45° (D) –135° |
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Answer» (A) is the correct answer. The equation of the line x – y + 3 = 0 can be rewritten as y = x + 3 ⇒ m = tan θ = 1 and hence θ = 45°. |
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| 54. |
Find the value of so that the three lines 3x+ y – 2 = 0, px+ 2y – 3 = 0 and 2x – y – 3 = 0 may intersect at one point. |
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Answer» The given equation of lines are 3x + y – 2 = 0 (1) 2x – y – 3 = 0 (2) px + 2y – 3 = 0 (3) Solving (1) and (2), we have (1) + (2) ⇒ 5x – 5 ⇒ x = 1 (1) ⇒ 3 + y – 2 = 0 ⇒ y = – 1 ∴ (1, – 1) is the point of intersection of (1) and (2) putting (1, – 1) in equation (3), we get, p. 1 + 2. (– 1) – 3 = 0 ⇒ p – 5 = 0 ⇒ p = 5 |
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| 55. |
Find the condition, if the two lines ax + by = c and a′x + b′y = c′ are perpendicular. |
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Answer» The given lines are ax + by = c ⇒ y = \(-\frac{ax}{b}+\frac{c}{b},m_1=-\frac{a}{b}\) and a'x +b'y = c' ⇒ y = \(\frac{a'}{b'}x+\frac{c'}{b'},m_2=-\frac{a'}{b'}\) Since the line are perpendicular. ∴ m1m2 = – 1 ⇒ (−\(\frac{a}{b}\) ) (−\(\frac{a'}{b'}\)) = − 1 ⇒ \(\frac{aa'}{bb'}=-1\) ⇒ aa′ + bb′ = 0, which is the required condition. |
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| 56. |
If a, b, c are in A.P., then the line ax + by + c = 0 passes through a fixed point. Write the coordinates of that point. |
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Answer» Given: a, b, c are in A.P. To find: The coordinates of that point. Explanation: If a, b, c are in A.P., then a + c = 2b ⇒ a – 2b + c = 0 Comparing the coefficient of ax + by + c = 0 and a – 2b + c = 0, we get x = 1 and y = -2 Hence, the coordinate of that point is (1, -2). |
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| 57. |
A line passes through the point (2, 2) and is perpendicular to the line 3x + y = 3. Its y-intercepts is A. \(\frac{1}{3}\) B. \(\frac{2}{3}\) C. 1 D. \(\frac{4}{3}\) |
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Answer» The equation of the line perpendicular to 3x + y = 3 is given below: x – 3y + λ = 0 This line passes through (2, 2). 2 – 6 + λ = 0 ⇒ λ = 4 So, the equation of the line will be x – 3y + 4 = 0 ⇒ y = 13x + 43 Hence, the y-intercept is \(\frac{4}{3}\). |
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| 58. |
Find the equation of the line: Containing the point A(3, 5) and having slope 2/3 |
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Answer» Given, slope(m) = 2/3 and the line passes through (3, 5). Equation of the line in slope point form is y-y1 = m(x -x1) ∴ The equation of the required line is y – 5 = 2/3 (x-3) ∴ 3 (y – 5) = 2 (x – 3) ∴ 3y – 15 = 2x – 6 ∴ 2x – 3y + 9 = 0 |
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| 59. |
A line passes through (2, 2) and is perpendicular to the line 3x + y = 3. Its y-intercept isA. 1/3B. 2/3C. 1D. 4/3 |
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Answer» Given line is 3x + y = 3 Now, we find the slope of given equation 3x + y = 3 It can be re-written as y = -3x + 3 Since, the above equation is in y = mx + b form So, the slope m = -3 Slope of perpendicular line = 1/3 So, the line passes through (2, 2) and having slope 1/3 is y - 2 = 1/3(x - 2) ⇒ 3y – 6 = x – 2 ⇒ 3y = x + 4 y = 1/3x + 4/3 [∵y = mx + c] So, the y – intercept is 4/3 Hence, the correct option is (d) |
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| 60. |
Write each of the following equations in ax + by + c = 0 form,i. y = 2x – 4ii. y = 4iii. x/2 + y/4 = 1iv. x/3 - y/2 = 0 |
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Answer» i. y = 2x – 4 ∴ 2x – y – 4 = 0 is the equation in ax + by + c = 0 form. ii. y = 4 ∴ 0x + 1y – 4 = 0 is the equation in ax + by + c = 0 form. iii. x/2 + y/4 = 1 ∴ 2x +y/4 ∴ 2x + y – 4 = 0 is the equation in ax + by + c = 0 form. iv. x/3 - y/2 = 0 ∴ 2x – 3y = 0 ∴ 2x – 3y + 0 = 0 is the equation in ax + by + c = 0 form. |
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| 61. |
Put the equation x/a + y/b = 1 the slope intercept form and find its slope and y – intercept. |
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Answer» Given: the equation is x/a + y/b = 1 We know that, General equation of line y = mx + c. bx + ay = ab ay = – bx + ab y = -bx/a + b The slope intercept form of the given line. ∴ Slope = – b/a and y – intercept = b |
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| 62. |
Find the equation of the line: Having slope 1/2 and containing the point (3, -2) |
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Answer» Given, slope(m) = 1/2 and the line passes through (3, – 2). Equation of the line in slope point form is y-y1 = m(x-x1) ∴ The equation of the required line is [y-(-2)] = 1/2 (x-3) ∴ 2(y + 2)=x – 3 ∴ 2y + 4 = x – 3 ∴ x – 2y – 7 = 0 |
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| 63. |
Find the equation of the line: Passing through the origin and parallel to AB, where A is (2,4) and B is (1,7). |
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Answer» Given, A (2, 4) and B (1, 7) Slope of AB = \(\frac {7-4}{1-2} =\)-3 1-2 Since the required line is parallel to line AB, slope of required line (m) = slope of AB ∴ m = – 3 and the required line passes through the origin. Equation of the line having slope m and passing through origin (0, 0) is y = mx. ∴ The equation of the required line is y = – 3x |
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| 64. |
Put the equation \(\frac{x}{a}+\frac{y}{b}=1\) the slope intercept form and find its slope and y - intercept. |
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Answer» Given: the equation is \(\frac{x}{a}+\frac{y}{b}=1\) Concept Used: General equation of line y = mx + c. Explanation: bx + ay = ab ⇒ ay = - bx + ab ⇒ y = \(-\frac{b}{a}\)x + b Hence, the slope intercept form of the given line. ∴ Slope = - b/a and y - intercept = b |
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| 65. |
Find the equation of the parallel to x–axis and passing through (3, – 5). |
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Answer» Given, A line which is parallel to x–axis and passing through (3, – 5) To Find: The equation of the line. Formula used: The equation of line is [y – y1 = m(x – x1)] Explanation: Here, The line is parallel to the x–axis, So, The parallel lines have equal slopes, And, the slope of x–axis is always 0, then The slope of line, m = 0 Coordinates of line are (x1, y1) = (3, – 5) The equation of line = y – y1 = m(x – x1) By putting the values, we get y – (– 5) = 0(x – 3) y + 5 = 0 Hence, The equation of line is y + 5 = 0 |
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| 66. |
Find the equation of a line for which p = 8, α = 225° |
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Answer» Given p = 8, α = 225° Concept Used: Equation of line in normal form. Explanation: So, the equation of the line in normal form is Formula Used: x cos α + y sin α = p x cos 225° + y sin 225° = 8 We know, cos (180° + θ) = – cos θ , sin (180° + θ) = – sin θ ⇒ – cos 45° – y sin 45° = 8 ⇒ \(-\frac{x}{\sqrt{2}}-\frac{y}{\sqrt{2}}=8\) ⇒ x + y + 8√2 = 0 Hence, the equation of line in normal form is x + y + 8√2 = 0 |
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| 67. |
Find the coordinates of the vertices of a triangle, the equations of whose sides are : x + y – 4 = 0, 2x – y + 3 0 and x – 3y + 2 = 0 |
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Answer» Given: x + y − 4 = 0, 2x − y + 3 = 0 and x − 3y + 2 = 0 To find: Point of intersection of pair of lines. Concept Used: Point of intersection of two lines. Explanation: x + y − 4 = 0 … (1) 2x − y + 3 = 0 … (2) x − 3y + 2 = 0 … (3) Solving (1) and (2) using cross - multiplication method: \(\frac{x}{3-4},\frac{y}{-8-3}=\frac{1}{-1-2}\) ⇒ \(x=\frac{1}{3},y=\frac{11}{3}\) Solving (1) and (3) using cross - multiplication method: \(\frac{x}{2-12},\frac{y}{-4-2}=\frac{1}{-3-1}\) ⇒ \(x=\frac{5}{2},y=\frac{3}{2}\) Similarly, solving (2) and (3) using cross - multiplication method: \(\frac{x}{-2+9}=\frac{y}{3-4}=\frac{1}{-6+1}\) ⇒ \(x=\frac{7}{5},y=\frac{1}{5}\) Hence, the coordinates of the vertices of the triangle are \(\Big(\frac{1}{3},\frac{11}{3}\Big)\) ,\(\Big(\frac{5}{2},\frac{3}{2}\Big)\) and \(\Big(-\frac{7}{5},\frac{1}{5}\Big)\) |
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| 68. |
Find the equation of a line for which p = 4, α = 150 |
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Answer» Given: p = 4, α = 150° Concept Used: Equation of line in normal form. Explanation: So, the equation of the line in normal form is Formula Used: x cos α + y sin α = p x cos 150° + y sin 150° = 4 cos (180° – θ) = – cos θ , sin (180° – θ) = sin θ ⇒ x cos(180° – 30°) + y sin(180° – 30°) = 4 ⇒ – x cos 30° + y sin 30° = 4 ⇒ \(\frac{\sqrt{3}x}{2}+\frac{y}{2}=4\) ⇒ √3x – y + 8 = 0 Hence, the equation of line in normal form is √3 x – y + 8 = 0 |
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| 69. |
The equation of the line passing through the point (1, 2) and perpendicular to the line x + y + 1 = 0 isA. y – x + 1 = 0B. y – x – 1 = 0C. y – x + 2 = 0D. y – x – 2 = 0 |
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Answer» B. y – x – 1 = 0 Explanation: Given that line passing through the point (1, 2) And perpendicular to the line x + y + 1 = 0 Let the equation of line ‘L’ is x – y + k = 0 … (i) Since, L is passing through the point (1, 2) ∴ 1 – 2 + k = 0 ⇒ k = 1 Putting the value of k in equation (i), we get x – y + 1 = 0 Or y – x – 1 = 0 Hence, the correct option is (b) |
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| 70. |
Find the equation of a line for which p = 5, α = 60° |
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Answer» Given: p = 5, α = 60° Concept Used: Equation of line in normal form. Explanation: So, the equation of the line in normal form is Formula Used: x cos α + y sin α = p x cos 60° + y sin 60° = 5 ⇒ \(\frac{x}{2}+\frac{\sqrt{3y}}{2}=5\) ⇒ x + √3y = 10 Hence, the equation of line in normal form is x + √3y = 10. |
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| 71. |
Find the equation to the straight line which cuts off equal positive intercepts on the axes and their product is 25. |
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Answer» Given: a = b and ab = 25 Let us find the equation of the line which cutoff intercepts on the axes. ∴ a2 = 25 a = 5 [considering only positive value of intercepts] By using the formula, The equation of the line with intercepts a and b is x/a + y/b = 1 x/5 + y/5 = 1 By taking LCM x + y = 5 |
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| 72. |
The equation of the straight line passing through the point (3, 2) and perpendicular to the line y = x isA. x – y = 5B. x + y = 5C. x + y = 1D. x – y = 1 |
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Answer» B. x + y = 5 Explanation: Given that straight line passing through the point (3, 2) And perpendicular to the line y = x Let the equation of line ‘L’ is y – y1 = m(x – x1) Since, L is passing through the point (3, 2) ∴ y – 2 = m(x – 3) … (i) Now, given eq. is y = x Since, the above equation is in y = mx + b form So, the slope of this equation is 1 It is also given that line L and y = x are perpendicular to each other. We know that, when two lines are perpendicular, then m1 × m2 = -1 ∴ m × 1 = -1 ⇒ m = -1 Putting the value of m in equation (i), we get y – 2 = (-1) (x – 3) ⇒ y – 2 = -x + 3 ⇒ x + y = 3 + 2 ⇒ x + y = 5 Hence, the correct option is (b) |
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| 73. |
Find the equation of the line on which the length of the perpendicular segment from the origin to the line is 4 and the inclination of the perpendicular segment with the positive direction of x–axis is 30°. |
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Answer» Given: p = 4, α = 30° The equation of the line in normal form is given by Using the formula, Now, substitute the values, we get x√3/2 + y1/2 = 4 ∴ The equation of line in normal form is √3x + y = 8. |
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| 74. |
Find the equation of a line, whose inclination is 150° with x-axis and passes through (3, – 5) |
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Answer» Inclination of the line, \(\theta\) = 150° ∴ Slope, m = tan(150°) = tan(90° + 60°) = – Cot 60° = – \(\frac{1}{\sqrt{3}}\) Since the line passes through (3, – 5) ∴ Equation of the line is (y – y0) = m(x – x0) ⇒ y − (−5) = −\(\frac{1}{\sqrt{3}}\) (x − 3) ⇒ √3(y + 5) = x – 3 ⇒ x + √3y + (5√3 − 3) = 0, is the required equation of the line. |
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| 75. |
Find the equation of a line for which(i) p = 5, α = 60°(ii) p = 4, α = 150° |
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Answer» (i) p = 5, α = 60° Given: p = 5, α = 60° The equation of the line in normal form is given by Using the formula, Now, substitute the values, we get x/2 + √3y/2 = 5 ∴ The equation of line in normal form is x + √3y = 10. (ii) p = 4, α = 150° Given: p = 4, α = 150° The equation of the line in normal form is given by Using the formula, Now, substitute the values, we get x cos 150° + y sin 150° = 4 cos (180° – θ) = – cos θ , sin (180° – θ) = sin θ x cos(180° – 30°) + y sin(180° – 30°) = 4 – x cos 30° + y sin 30° = 4 –√3x/2 + y/2 = 4 -√3x + y = 8 ∴ The equation of line in normal form is -√3x + y = 8. |
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| 76. |
Find the equations of the straight lines which pass through (4, 3) and are respectively parallel and perpendicular to the x–axis. |
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Answer» Given: A line which is perpendicular and parallel to x–axis respectively and passing through (4, 3) By using the formula, The equation of line: [y – y1 = m(x – x1)] Let us consider, Case 1: When Line is parallel to x–axis The parallel lines have equal slopes, And, the slope of x–axis is always 0, then The slope of line, m = 0 Coordinates of line are (x1, y1) = (4, 3) The equation of line is y – y1 = m(x – x1) Now substitute the values, we get y – (3) = 0(x – 4) y – 3 = 0 Case 2: When line is perpendicular to x–axis The line is perpendicular to the x–axis, then x is 0 and y is – 1. The slope of the line is, m = y/x = -1/0 Coordinates of line are (x1, y1) = (4, 3) The equation of line = y – y1 = m(x – x1) Now substitute the values, we get y – 3 = (-1/0) (x – 4) ∴ The equation of line when it is parallel to x – axis is y = 3 and it is perpendicular is x = 4. |
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| 77. |
If a point P(x, y) is equidistant from the points A(6, -1) and B(2, 3), find the relation between x and y. |
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Answer» Given: Point P(x, y) is equidistant from points A(6, -1) and B(2, 3) i.e., distance of P from A = distance of P from B ⇒ \(\sqrt{(x-6)^2+(y+1)^2}\) = \(\sqrt{(x-2)^2+(y-3)^2}\) Squaring both sides, ⇒ (x – 6)2 + (y – 1)2 = (x – 2)2 + (y – 3)2 ⇒ x2 – 12x + 36 + y2 – 2y + 1 = x2 – 4x + 4 + y2 – 6y + 9 ⇒ –12x + 36 + 2y + 1 = – 4x + 4 – 6y + 9 ⇒ – 8x + 8y = –24 ⇒ x – y = 3 Therefore, x – y = 3 is the required relation. |
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| 78. |
Find the equation of a line equidistant from the lines y = 10 and y = – 2. |
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Answer» A line which is equidistant from the lines y = 10 and y = – 2 To Find: The equation of the line Formula used: The equation of line is [y – y1 = m(x – x1)] Explanation: A line which is equidistant from, two other lines, So, the slopes must be the same . Therefore, The slope of line y = 10 and y = – 2 is 0, because lines are parallel to the x–axis. Since, The required line will pass from the midpoint of the line joining (0, – 2) and (0, 10) The Midpoint formula = \(\Big[\frac{x+x_1}{2},\frac{y+y_1}{2}\Big]\) So, The coordinates of the point will be \(\Big[0,\frac{10-2}{2}\Big]\) (0, 4) Since The equation of the line is : y – 4 = 0(x – 0) y = 4 Hence, The equation of the line is y = 4 |
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| 79. |
Find the equation of a line making an angle of 150° with the x–axis and cutting off an intercept 2 from y–axis. |
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Answer» Given: A line which makes an angle of 150° with the x–axis and cutting off an intercept at 2 By using the formula, The equation of a line is y = mx + c We know that angle, θ = 150° The slope of the line, m = tan θ Where, m = tan 150° = -1/ √3 Coordinate of y–intercept is (0, 2) The required equation of the line is y = mx + c Now substitute the values, we get y = -x/√3 + 2 √3y – 2√3 + x = 0 x + √3y = 2√3 ∴ The equation of line is x + √3y = 2√3 |
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| 80. |
Find the equation of a straight line:(i) with slope 2 and y – intercept 3;(ii) with slope – 1/ 3 and y – intercept – 4.(iii) with slope – 2 and intersecting the x–axis at a distance of 3 units to the left of origin. |
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Answer» (i) Here, The slope is 2 and the coordinates are (0, 3) Now, The required equation of line is y = mx + c y = 2x + 3 (ii) Here, The slope is – 1/3 and the coordinates are (0, – 4) Now, The required equation of line is y = mx + c y = -\(\frac{1}{3}\) x – 4 3y + x = – 12 (iii) Here, The slope is – 2 and the coordinates are (– 3, 0) Now, The required equation of line is y – y1 = m (x – x1) y – 0 = – 2(x + 3) y = – 2x – 6 2x + y + 6 = 0 |
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| 81. |
Find the equation of a line, which is equidistant from y = – 3 and y = 13. |
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Answer» The given lines are y = – 3 and y = 13. So, the resulting line is also of the form y = a, where a = \(\frac{− 3 + 13}{2}\) = 5 ∴ The resulting line is y = 5. |
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| 82. |
Find the equation of a straight line:(i) with slope 2 and y – intercept 3;(ii) with slope – 1/ 3 and y – intercept – 4.(iii) with slope – 2 and intersecting the x–axis at a distance of 3 units to the left of origin. |
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Answer» (i) With slope 2 and y – intercept 3 The slope is 2 and the coordinates are (0, 3) Now, the required equation of line is y = mx + c Substitute the values, we get y = 2x + 3 (ii) With slope – 1/ 3 and y – intercept – 4 The slope is – 1/3 and the coordinates are (0, – 4) Now, the required equation of line is y = mx + c Substitute the values, we get y = -1/3x – 4 3y + x = – 12 (iii) With slope – 2 and intersecting the x–axis at a distance of 3 units to the left of origin The slope is – 2 and the coordinates are (– 3, 0) Now, the required equation of line is y – y1 = m (x – x1) Substitute the values, we get y – 0 = – 2(x + 3) y = – 2x – 6 2x + y + 6 = 0 |
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| 83. |
Find the equation of a line which is parallel to y-axis and passes through (– 4, 3). |
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Answer» Equation of a line parallel to y-axis is x = a x = a Since the line passes through the point (– 4, 3). ∴ – 4 = a ⇒ a = – 4. ∴ The equation of the line is x = – 4. |
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| 84. |
Find the equation of the line which cuts intercepts 2 units and 5 units from x-axis and y-axis respectively. |
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Answer» Equation of a line in intercepts form is \(\frac{x}{a}\) + \(\frac{y}{b}\) = 1 …(i) Given, a = 2 and b = 5 ∴ (1) ⇒ \(\frac{x}{2}\) + \(\frac{y}{5}\) = 1 ⇒ 5x + 2y – 10 = 0, is the required equation of the line. |
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| 85. |
Obtain the equation of the line containing the point: B(4, – 3) and parallel to the X-axis. |
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Answer» Equation of a line parallel to X-axis is of the form y = k. Since the line passes through B(4, – 3), k = -3 ∴ The equation of the required line is y = – 3. |
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| 86. |
Find the equation of the line passing through the points (2, 2) and (4, – 6). |
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Answer» Equation of a line in two point form is y − y1 = \(\frac{y_2 − y_1}{x_2 − x_1}\) (x − x1) …(i) Given, x1 = 2, x2 = 4, y1 = 2, y2 = – 6 ⇒ y − 2 = \(\frac{-6 − 2}{4 − 2}\) (x − 2) ⇒ y – 2 = – 4 (x – 2) ⇒ 4x + y – 10 = 0, is the required equation of the line. |
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| 87. |
Obtain the equation of the line containing the point: (2, 3) and parallel to the X-axis. |
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Answer» Equation of a line parallel to X-axis is of the form y = k. Since the line passes through (2, 3), k = 3 ∴ The equation of the required line is y = 3. |
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| 88. |
If A(2, -5), B(-2, 5), C(x, 3) and D(1, 1) be four points such that AB and CD are perpendicular to each other, find the value of x. |
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Answer» For two lines to be perpendicular, their product of slope must be equal to -1. Given points are A(2, -5),B(-2, 5) and C(x, 3),D(1, 1) slope = (y2-y1/x2-x1) ⇒ Slope of line AB is equal to (5+5/-2-2) = (10/-4) = (-5/2) = -2.5 And the slope of line CD is equal to (1-3/1-x) = (-2/1-x) Their product must be equal to -1 the slope of line AB×Slope of line CD = -1 ⇒ -2.5 x (-2/1-x) = -1 ⇒ 5 = x-1 ⇒x = 6 |
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| 89. |
What can be said regarding a line if its slope is (i) zero (ii) positive (iii) negative |
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Answer» (i) If the slope of the line is zero it means M = tan θ M = tan 0 Since, m = 0 So, The line is parallel to x - axis. (ii) If the slope of the line is positive it means Since θ is an acute So, The line makes an acute angle with the positive x - axis. (iii) If the slope of the line is positive it means Since, θ is an obtuse So, The line makes an obtuse angle with positive x - axis. |
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| 90. |
What is the value of y so that the line through (3, y) and (2, 7) is parallel to the line through (– 1, 4) and (0, 6) ? |
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Answer» We have given coordinates of two lines (3, y) and (2, 7), (– 1, 4) and (0, 6) To Find: Value of y? The concept used: Slopes of the parallel line are always equal. The formula used: The slope of line = \(\frac{y_2-y_1}{x_2-x_1}\) Now, The slope of the line whose coordinates are (3, y) and (2, 7). M1 = \(\frac{7-y}{2-3}\) …… (1) And, Now, The slope of the line whose coordinates are (– 1, 4) and (0, 6). M2 = \(\frac{6-4}{0-(-1)}\) M2 = \(\frac{2}{1}\)…… (2) On equating the equation (1) and (2), we get \(\frac{7-y}{2-3}=\frac{2}{1}\) 7 – y = 2(– 1) – y = – 2 – 7 Y = 9 Hence, The value of y is 9. |
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| 91. |
Find the separate equation of the lines represented by the following equation :10(x + 1)2 + (x + 1)( y – 2) – 3(y – 2)2 = 0 |
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Answer» 10(x + 1)2 + (x + 1)( y – 2) – 3(y – 2)2 = 0 …(1) Put x + 1 = X and y – 2 = Y ∴ (1) becomes 10x2 + xy – 3y2 = 0 10x2 + 6xy – 5xy – 3y2 = 0 2x(5x + 3y) – y(5x + 3y) = 0 (2x – y)(5x + 3y) = 0 5x + 3y = 0 and 2x – y = 0 5x + 3y = 0 5(x + 1) + 3(y – 2) = 0 5x + 5 + 3y – 6 = 0 ∴ 5x + 3y – 1 = 0 2x – y = 0 2(x + 1) – (y – 2) = 0 2x + 2 – y + 2 = 0 ∴ 2x – y + 4 = 0 |
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| 92. |
Find the equation of the line with slope ‘5’ and y-intercept ‘3’ above the x- axis. |
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Answer» Equation of a line in slope-intercept form is y = mx + c Also, c = 3 and m = 5 ∴ (1) ⇒ y = 5x + 3, is the required equation of the line. |
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| 93. |
What is the value of y, so that the line through (3, y) and (2, 7), is parallel to the line through (– 1, 4) and (0, 6)? |
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Answer» Slope of the line segment passing through (3, y) and (2, 7), m1 = \(\frac{7 − y}{2 − 3}\) = y – 7 And slope of the line passing through (– 1, 4) and (0, 6) m2 = \(\frac{6 − 4}{0 + 1}\) = 2 Since, the lines are parallel, So m1 = m2 ⇒ y – 7 = 2 ⇒ y = 9 |
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| 94. |
Find the slope of the line 6x + 3y – 5 = 0. |
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Answer» Given line is 6x + 3y – 5 = 0 ⇒ 3y = – 6x + 5 ⇒ y = – 2x + \(\frac{5}{3}\) ∴ Slope = – 2. |
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| 95. |
Find the separate equation of the lines represented by the following equation :(x – 2)2 – 3(x – 2)(y + 1) + 2(y + 1)2 = 0 |
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Answer» (x – 2)2 – 3(x – 2)(y + 1) + 2(y + 1)2 = 0 ∴ (x – 2)2 – 2(x – 2)(y + 1) – (x – 2)(y + 1) + 2(y + 1)2 = 0 ∴ (x – 2) [(x – 2) – 2(y + 1)] – (y + 1)[(x – 2) – 2(y + 1)] = 0 ∴ (x – 2)(x – 2 – 2y – 2) – (y + 1)(x – 2 – 2y – 2) = 0 ∴ (x – 2)(x – 2y – 4) – (y + 1)(x – 2y – 4) = 0 ∴ (x – 2y – 4)(x – 2 – y – 1) = 0 ∴ (x – 2y – 4)(x – y – 3) = 0 ∴ the separate equations of the lines are x – 2y – 4 = 0 and x – y – 3 = 0. Alternative Method : (x – 2)2 – 3(x – 2)(y + 1) + 2(y + 1)2 = 0 … (1) Put x – 2 = X and y + 1 = Y ∴ (1) becomes, X2 – 3XY + 2Y2 = 0 ∴ X2 – 2XY – XY + 2Y2 = 0 ∴ X(X – 2Y) – Y(X – 2Y) = 0 ∴ (X – 2Y)(X – Y) = 0 ∴ the separate equations of the lines are ∴ X – 2Y = 0 and X – Y = 0 ∴ (x – 2) – 2(y + 1) = 0 and (x – 2) – (y +1) = 0 ∴ x – 2y – 4 = 0 and x – y – 3 = 0. |
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| 96. |
Find the acute angle between the lines 2x – y + 3 = 0 and x + y + 2 = 0. |
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Answer» Given: The equations of the lines are 2x − y + 3 = 0 … (1) x + y + 2 = 0 … (2) Let m1 and m2 be the slopes of these lines. m1 = 2, m2 = -1 Let θ be the angle between the lines. tan θ = [(m1 – m2) / (1 + m1m2)] = [(2 + 1) / (1 + 2)] = 3 θ = tan-1 (3) ∴ The acute angle between the lines is tan-1 (3). |
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| 97. |
Find the angles between each of the following pairs of straight lines:(i) 3x + y + 12 = 0 and x + 2y – 1 = 0(ii) 3x – y + 5 = 0 and x – 3y + 1 = 0 |
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Answer» (i) 3x + y + 12 = 0 and x + 2y – 1 = 0 Given: The equations of the lines are 3x + y + 12 = 0 … (1) x + 2y − 1 = 0 … (2) Let m1 and m2 be the slopes of these lines. m1 = -3, m2 = -1/2 Let θ be the angle between the lines. tan θ = [(m1 – m2) / (1 + m1m2)] = [(-3 + 1/2) / (1 + 3/2)] = 1 θ = π/4 or 45o ∴ The acute angle between the lines is 45° (ii) 3x – y + 5 = 0 and x – 3y + 1 = 0 Given: The equations of the lines are 3x − y + 5 = 0 … (1) x − 3y + 1 = 0 … (2) Let m1 and m2 be the slopes of these lines. m1 = 3, m2 = 1/3 Let θ be the angle between the lines. tan θ = [(m1 – m2) / (1 + m1m2)] = [(3 + 1/3) / (1 + 1)] = 4/3 θ = tan-1 (4/3) ∴ The acute angle between the lines is tan-1 (4/3). |
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| 98. |
Find the equation of a line which is perpendicular to the line√3x – y + 5 = 0 and which cuts off an intercept of 4 units with the negative direction of y-axis. |
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Answer» Given: The equation is perpendicular to √3x – y + 5 = 0 equation and cuts off an intercept of 4 units with the negative direction of y-axis. The line perpendicular to √3x – y + 5 = 0 is x + √3y + λ = 0 It is given that the line x + √3y + λ = 0 cuts off an intercept of 4 units with the negative direction of the y-axis. This means that the line passes through (0,-4). So, Let us substitute the values in the equation x + √3y + λ = 0, we get 0 – √3 (4) + λ = 0 Now, substitute the value of λ back, we get x + √3y + 4√3 = 0 ∴ The required equation of line is x + √3y + 4√3 = 0. |
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| 99. |
Find the equation of the line which intersects the x-axis at a distance of 3 units to the left of origin with slope –2. |
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Answer» It is known that if a line with slope m makes x-intercept d, then the equation of the line is given as y = m(x – d) |
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| 100. |
Find the equation of the right bisector of the line segment joining the points (a, b) and (a1, b1). |
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Answer» Given: A (a, b) and B (a1, b1) be the given points To find: Equation of the right bisector of the line segment joining the points (a, b) and (a1, b1). Explanation: Let C be the midpoint of AB. ∴ coordinates of C = \(\Big(\frac{a+a_2}{2},\frac{b+b_1}{2}\Big)\) And, slope of AB = \(\frac{b_1-b}{a_1-a}\) So, the slope of the right bisector of AB is \(-\frac{a_1-a}{b_1-b}\) Thus, the equation of the right bisector of the line segment joining the points (a, b) and (a1, b1) is \(y - \frac{b+b_1}{2}\) = \(-\frac{a_1-a}{b_1-b}\Big(x-\frac{a+a_1}{2}\Big)\) ⇒ 2 (a1 - a)x + 2y(b1 - b) + (a2 + b2) – (a12 + b12) = 0 Hence, equation of the required line 2 (a1 – a)x + 2y(b1- b) + (a2 + b2) – (a12 + b12) = 0 |
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