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51.

Define concurrent lines

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. 

52.

Write the coordinates of the orthocenter of the triangle formed by the lines xy = 0 and x + y = 1

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).

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°

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°.

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.

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

55.

Find the condition, if the two lines ax + by = c and a′x + b′y = c′ are perpendicular.

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.

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.

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).

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. \(\frac{4}{3}\) 

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 \(\frac{4}{3}\).

58.

Find the equation of the line: Containing the point A(3, 5) and having slope 2/3

Answer»

Given, slope(m) = 2/3  and the line passes through (3, 5).

Equation of the line in slope point form is y-y= 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

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

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)

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

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.

61.

Put the equation x/a + y/b = 1 the slope intercept form and find its slope and y – intercept.

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

62.

Find the equation of the line: Having slope 1/2 and containing the point (3, -2)

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

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).

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

64.

Put the equation \(\frac{x}{a}+\frac{y}{b}=1\) the slope intercept form and find its slope and y - intercept. 

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

65.

Find the equation of the parallel to x–axis and passing through (3, – 5).

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

66.

Find the equation of a line for which p = 8, α = 225°

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 

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

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 \(\Big(-\frac{7}{5},\frac{1}{5}\Big)\)

68.

Find the equation of a line for which p = 4, α = 150

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

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

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)

70.

Find the equation of a line for which p = 5, α = 60°

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.

71.

Find the equation to the straight line which cuts off equal positive intercepts on the axes and their product is 25.

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
∴ The equation of line is x + y = 5

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

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)

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°.

Answer»

Given:

p = 4, α = 30°

The equation of the line in normal form is given by

Using the formula,
x cos α + y sin α = p

Now, substitute the values, we get
x cos 30° + y sin 30° = 4

x3/2 + y1/2 = 4
√3x + y = 8

∴ The equation of line in normal form is √3x + y = 8.

74.

Find the equation of a line, whose inclination is 150° with x-axis and passes through (3, – 5)

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.

75.

Find the equation of a line for which(i) p = 5, α = 60°(ii) p = 4, α = 150°

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,
x cos α + y sin α = p

Now, substitute the values, we get
x cos 60° + y sin 60° = 5

x/2 + 3y/2 = 5
x + √3y = 10

∴ 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,
x cos α + y sin α = p

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.

76.

Find the equations of the straight lines which pass through (4, 3) and are respectively parallel and perpendicular to the x–axis.

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)
x = 4

∴ The equation of line when it is parallel to x – axis is y = 3 and it is perpendicular is x = 4.

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.

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.

78.

Find the equation of a line equidistant from the lines y = 10 and y = – 2.

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

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.

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 – 23 + x = 0

x + 3y = 23

∴ The equation of line is x + 3y = 23

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.

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

81.

Find the equation of a line, which is equidistant from y = – 3 and y = 13.

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.

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.

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

83.

Find the equation of a line which is parallel to y-axis and passes through (– 4, 3).

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.

84.

Find the equation of the line which cuts intercepts 2 units and 5 units from x-axis and y-axis respectively.

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.

85.

Obtain the equation of the line containing the point: B(4, – 3) and parallel to the X-axis.

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.

86.

Find the equation of the line passing through the points (2, 2) and (4, – 6).

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.

87.

Obtain the equation of the line containing the point: (2, 3) and parallel to the X-axis.

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.

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.

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

89.

What can be said regarding a line if its slope is (i) zero (ii) positive (iii) negative

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.

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) ?

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.

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

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

92.

Find the equation of the line with slope ‘5’ and y-intercept ‘3’ above the x- axis.

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.

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)?

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

94.

Find the slope of the line 6x + 3y – 5 = 0.

Answer»

Given line is 6x + 3y – 5 = 0

⇒ 3y = – 6x + 5

⇒ y = – 2x + \(\frac{5}{3}\)

∴ Slope = – 2.

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

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.

96.

Find the acute angle between the lines 2x – y + 3 = 0 and x + y + 2 = 0.

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.
Then, by using the formula

tan θ = [(m1 – m2) / (1 + m1m2)]

= [(2 + 1) / (1 + 2)]

= 3
So,

θ = tan-1 (3)

∴ The acute angle between the lines is tan-1 (3).

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

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.
Then, by using the formula

tan θ = [(m1 – m2) / (1 + m1m2)]

= [(-3 + 1/2) / (1 + 3/2)]

= 1

So,

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.
Then, by using the formula

tan θ = [(m1 – m2) / (1 + m1m2)]

= [(3 + 1/3) / (1 + 1)]

= 4/3

So,

θ = tan-1 (4/3)

∴ The acute angle between the lines is tan-1 (4/3).

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.

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 
λ = 4√3

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.

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.

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)
For the line intersecting the x-axis at a distance of 3 units to the left of the origin,
d = –3.
The slope of the line is given as m = –2
Thus, the required equation of the given line is y = –2 [x – (–3)] y = –2x – 6
i.e., 2x + y + 6 = 0

100.

Find the equation of the right bisector of the line segment joining the points (a, b) and (a1, b1).

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(b- b) + (a2 + b2) – (a12 + b12) = 0 

Hence, equation of the required line 2 (a1 – a)x + 2y(b1- b) + (a2 + b2) – (a12 + b12) = 0