

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. |
Determine whether the given values are solutions of the given equation or not:2x2 – x + 9 = x2 + 4x + 3, x = 2, x = 3 |
Answer» Here we have, 2x2 – x + 9 = x2 + 4x + 3 ⇒ x2 – 5x + 6 = 0 LHS = x2 – 5x + 6 Substituting x = 2 in LHS, we get (2)2 – 5(2) + 6 ⇒ 4 – 10 + 6 = 0 = RHS ⇒ LHS = RHS Thus, x = 2 is a solution of the given equation. Similarly, Substituting x = 3 in LHS, we get (3)2 – 5(3) + 6 ⇒ 9 – 15 + 6 = 0 = RHS ⇒ LHS = RHS Thus, x = 3 is a solution of the given equation. |
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52. |
Is the following statement ‘True’ or ‘False’?Justify your answer. If in a quadratic equation the coefficient of x is zero, then the quadratic equation has no real roots. |
Answer» False, since the discriminant in this case is – 4ac which can still be non-negative if a and c are of opposite signs or if one of a or c is zero. |
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53. |
Find the nature of the roots of the quadratic equation 3x2 – 2√6 x + 2 = 0. |
Answer» 3x2 – 2√6 x + 2 = 0 Compare given equation with the general form of quadratic equation, which is ax2 + bx + c = 0 a = 3, b = – 2√6, c = 2 Using Discriminant Formula: D = b2 – 4ac = (– 2√6)2 – 4 x 3 x 2 = 24 – 24 = 0 Roots of equation are real and equal. |
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54. |
If α, β, γ are the roots of the equation 2x3 – 3x2 + 6x + 1 = 0, then α2 +β2+ γ2 is equal to(a) \(\frac{-15}{4}\)(b) \(\frac{-9}{4}\)(c) \(\frac{13}{4}\)(d) 4 |
Answer» (a) \(\frac{-15}{4}\) Given,α, β, γ are the roots of the 2x3 – 3x2 + 6x + 1 = 0 Since S1 = \(\frac{\text{Coefficient of}\,x^2}{\text{Coefficient of}\,x^3}\) = S1 = α + β + γ = \(-\big(\frac{-3}{2}\big)\) = \(\frac{3}{2}\) Since S2 = \(\frac{\text{Coefficient of}\,x}{\text{Coefficient of}\,x^3}\) = S2 = αβ + βγ + αγ = \(\frac{6}{2}\) = 3 Since S3 = \(\frac{\text{Coefficient of constant term}}{\text{Coefficient of}\,x^3}\) = S3 = αβγ = \(-\frac12\) Now, α2 +β2+ γ2 = (α +β + γ)2 - 2(αβ + βγ + αγ) = \(\big(\frac{3}{2}\big)^2\) - 2 x 3 = \(\frac{9}{4}-6\) = \(\frac{-15}{4}\) |
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55. |
If an integer P is chosen at random in the interval 0 ≤ p ≤ 5, the probability that the roots of the equation x2 + px + \(\frac{p}{4}+\frac{1}{2}\) = 0 are real is(a) \(\frac{2}{3}\) (b) \(\frac{2}{5}\)(c) \(\frac{3}{5}\) (d) \(\frac{4}{5}\) |
Answer» (a) \(\frac{2}{3}\) The equation x2 + px + \(\frac{p}{4}+\frac{1}{2}\) = 0 has real roots if the discriminant D ≥ 0. ⇒ p2 – 4 \(\bigg(\frac{p}{4}+\frac{1}{2}\bigg)\)≥ 0 ⇒ p2 - p - 2 ≥ 0 ⇒ p2 – 2p + p – 2 ≥ 0 ⇒ p(p – 2) + 1 (p – 2) ≥ 0 ⇒ (p – 2) (p + 1) ≥ 0 ⇒ (p – 2) ≥ 0 and (p + 1) ≥ 0 ⇒ p ≥ 2 or p ≤ –1 The condition p ≤ –1 is not admissible as 0 ≤ p ≤ 5. Now p ≥ 2 ⇒ p can take up the value 2 or 3 or 4 or 5 from the given values. {0, 1, 2, 3, 4, 5} ∴ Probability (Roots of given equation are real) = \(\frac{\text{Number of values p can take}}{\text{Given number of values}}\) = \(\frac{4}{6}=\frac{2}{3}.\) |
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56. |
The number of solutions of x2 + |x - 1| = 1 is A. 0 B. 1 C. 2 D. 3 |
Answer» when x > 0 x2 + x-1 = 1 x2 + x - 2 = 0 (x-1) (x+2) = 0 x = 1, -2 when x < 0 x2 - x+1 = 1 x2 – x = 0 x(x-1) = 0 x = 0, 1 hence the given equation has 3 solutions and they are x = 0, 1, -1. |
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57. |
For what value of k will the roots of the equation kx2 – 5x + 6 = 0 be in the ratio 2 : 3 ?(a) 0 (b) 1 (c) –1 (d) 2 |
Answer» (b) 1 Let the roots of the equation kx2 – 5x + 6 = 0 be α and β. Then, α + β = \(\frac{5}{k}\) ...(i) αβ = \(\frac{6}{k}\) ...(ii) Given \(\frac{α}{β}\) = \(\frac{2}{3}\) ⇒ α = \(\frac{2}{3}\)β ∴ From (i) and (ii), \(\frac{2}{3}\)β + β = \(\frac{5}{k}\) and \(\frac{2}{3}\)β2 = \(\frac{6}{k}\) ⇒ \(\frac{5}{3}\)β = \(\frac{5}{k}\) and β2 = \(\frac{9}{k}\) ⇒ β = \(\frac{3}{k}\) and β2 = \(\frac{9}{k}\) ⇒ \(\frac{9}{k^2}\) = \(\frac{9}{k}\) ⇒ 9k2 - 9k = 0 k(k - 1) = 0 ⇒ k = 0 or 1 But k = 0 does not satisfy the condition, so k = 1. |
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58. |
In each of the following, determine whether the given values are solutions of the given equation or not:(i) \(x^{2}-3x+2=0,x=2,x=1\) (ii) \(x^{2}+x+1=0,x=0,x=1\)(iii) \(x^{2}-3\sqrt{3}+6=0,x=\sqrt{3},x=-2\sqrt{3}\)(iv) \(x+\frac{1}{x}=\frac{13}{6},x=\frac{5}{6},x=\frac{4}{3}\)(v) \(2x^{2}-x+9=x^{2}+4x+3,x=2,x=3\)(vi) \(x^{2}-\sqrt{2}x-4=0,=-\sqrt{2},x=-2\sqrt{2}\)(vii) \(a^{2}x^{2}-3abx+2b^{2}=0,x=a/b,x=b/a\) |
Answer» (i) \(x^{2}-3x+2=0,x=2,x=1\) For x = 2, 22 – 3 × 2 + 2 = 0 ⇒ 0 = 0 Thus, x = 2 is a solution. For, x = 1 12 – 3 × 1 + 2 = 0 ⇒ 0 = 0 Thus, x = 1 is a solution. (ii) \(x^{2}+x+1=0,x=0,x=1\) For x = 0, ⇒ 0 + 0 + 1 = 0 ⇒ 1 = 0 which is not true thus x = 0 is not a solution For x = 1, ⇒ 1 + 1 + 1 = 0 ⇒ 3 = 0 which is not true thus x = 1 is not a solution (iii) \(x^{2}-3\sqrt{3}+6=0,x=\sqrt{3},x=-2\sqrt{3}\) For x= √3 ⇒ 3 – 3√3 × √3 + 6 = 0 ⇒ 3 – 9 + 6 = 0 ⇒ 0 = 0 Thus, x = √3 is a solution For x = -2√3 ⇒ (-2√3)2 – 3√3 × -2√3 + 6 = 0 ⇒ 4 × 3 + 18 + 6 = 0 ⇒ 36 = 0 which is not true, thus x = -2√3 is not a solution (iv) \(x+\frac{1}{x}=\frac{13}{6},x=\frac{5}{6},x=\frac{4}{3}\) For x = 5/6 \(\Rightarrow \frac{5}{6}+\frac{6}{5}=\frac{13}{6}\) \(\Rightarrow \frac{61}{30}=\frac{13}{6}\) ⇒ 61 = 65 which is not true, thus x = 5/6 is not a solution For x = 4/3 \(\Rightarrow\frac{4}{3}+\frac{3}{4}=\frac{13}{6}\) ⇒ 25/12 = 13/6 ⇒ 25 = 26 which is not true, thus x = 4/3 is not a solution (v) \(2x^{2}-x+9=x^{2}+4x+3,x=2,x=3\) For x = 2, ⇒ 2 × 4 – 2 + 9 = 4 + 4 × 2 + 3 ⇒ 15 = 15, thus x = 2 is a solution. For x = 3 ⇒ 2 × 9 – 3 + 9 = 9 + 4 × 3 + 3 ⇒ 24 = 24, thus x = 3 is also a solution (vi) \(x^{2}-\sqrt{2}x-4=0,=-\sqrt{2},x=-2\sqrt{2}\) For x = -√2, ⇒ 2 - √2 × -√2 – 4 = 0 ⇒ 2 + 2 – 4 = 0 ⇒ 0 = 0 Thus, x = -√2 is a solution For x = -2√2 ⇒ 4 × 2 - √2 × -2√2 – 4 = 0 ⇒ 8 + 8 – 4 = 0 ⇒ 12 = 0 which is not true, thus x = -2√2 is not a solution (vii) \(a^{2}x^{2}-3abx+2b^{2}=0,x=a/b,x=b/a\) For, x = a/b \(\Rightarrow a^{2}\times\frac{a^{2}}{b^{2}}-3ab\times\frac{a}{b}+2\times b^{2}=0\) ⇒ a4/b2 – 3a2 + 2b2 = 0 which is not true, thus x = a/b is not a solution For x = b/a \(\Rightarrow a^{2}\times\frac{a^{2}}{b^{2}}-3ab\times\frac{b}{a}+2 b^{2}=0\) ⇒ b2 – 3b2 + 2b2 = 0 ⇒ 0 = 0 , thus x = b/a is a solution |
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59. |
Does (x – 1)2 + 2(x + 1) = 0 have a real root? Justify your answer. |
Answer» No, since the equation is simplified to x2 + 3 = 0 whose discriminant is –12. |
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60. |
A quadratic equation with integral coefficient has integral roots. Justify your answer. |
Answer» No, a quadratic equation with integral coefficients may or may not have integral roots. Justification Consider the following equation, 8x2 – 2x – 1 = 0 The roots of the given equation are ½ and – ¼ which are not integers. Hence, a quadratic equation with integral coefficient might or might not have integral roots. |
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61. |
2x2 - 7x + 6 = 0 check whether x = 3/2. |
Answer» Put x = 3/2 in the polynomial 2x2 - 7x + 6 = 2x2 - 7x + 6 = 2 (3/2)2 - 7(3/2) + 6 = 2 x 9/4 - 21/2 + 6 = 9/2 - 21/2 + 6 = (9 - 21 + 12)/2 = (21-21)/2 = 0 x = 3/2 is a solution of the equation. |
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62. |
If α and β are the roots of a quadratic equation ax2 + bx + c = 0 then α + β = ………(A) -b/a(B) b/2a(C) -b2 /4a(D) b2/4a |
Answer» The correct option is (A) -b/a If α and β are the roots of a quadratic equation ax2 + bx + c = 0 then α + β = -b/a. |
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63. |
If the roots of the equation a(b – c) x2 + b(c – a)x + c(a – b) = 0 are equal, then a, b, c are in :(a) AP (b) GP (c) HP (d) None of these |
Answer» (c) HP If the roots of the equation a(b – c)x2 + b(c – a)x + c(a – b) = 0 are equal, then Discriminant (D) = 0, i.e., ⇒ b2 (c – a)2 – 4a(b – c) c(a – b) = 0. ⇒ b2 (c2 + a2 – 2ac) – 4ac (ab – ca – b2 + bc) = 0 ⇒ b2c2 + b2 a2 – 2ab2c – 4a2bc + 4a2c2 + 4ab2c – 4abc2 = 0 ⇒ a2b2 + b2c2 + 4a2c2 + 2ab2c – 4a2bc – 4abc2 = 0 ⇒ (ab + bc – 2ac)2 = 0 ⇒ ab + bc – 2ac = 0 ⇒ ab + bc = 2ac ⇒ \(\frac{1}{c}+\frac{1}{a}=\frac{2}{b}\) ⇒ a, b, c are in H.P. |
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64. |
The values of x which satisfy the expression \((5+2\sqrt6)^{x^2+3}\) + \((5-2\sqrt6)^{x^2-3}\)= 10 are :(a) ± 2, ± √3 (b) ± √2, ± 4 (c) ± 2, ± √2 (d) 2, √2, √3 |
Answer» (c) ± 2, ± √2 Let y = 5 + 2√6. Then \(\frac{1}{y}\) = 5 - 2√6. Thus the given expression reduces to \(y^{x^2-3}\) + \(\big(\frac{1}{y}\big)^{x^2-3}\) = 10 Again let \(y^{x^2-3}\) = t. Then, t + \(\frac{1}{t}\) = 10 ⇒ t2 - 10t + 1 = 0 ⇒ t = \(\frac{10±\sqrt{100-4}}{2}\) = \(\frac{10 ±\sqrt{96}}{2}\) = \(\frac{10 ±4\sqrt{6}}{2}\) = 5 ± 2√6 \((5+2\sqrt6)^{x^2-3}\) = 5 ± 2√6 = (5 ± 2√6)±1 ⇒ x2 – 3 = 1 or x2 – 3 = – 1 ⇒ x2 = 4 or x2 = 2 ⇒ x = ± 2 or x = ± √2 |
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65. |
If α and β are the roots of a quadratic equation ax2 + bx + c = 0 then α + β = ………(A) -b/a(B) b/2a(C) -b2 /4a(D) b2/4a |
Answer» Answer: (A) -b/a If α and β are the roots of a quadratic equation ax2 + bx + c = 0 then α + β = -b/a. |
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66. |
The number of real solutions of the equation 2|x|2 – 5|x| + 2 = 0 is :(a) 0 (b) 4 (c) 2 (d) None of these |
Answer» (b) 4 2| \(x\) |2 – 5| \(x\) | + 2 = 0 ⇒ (2| \(x\) | – 1) (| \(x\) | – 2) = 0 ⇒ | \(x\) | = \(\frac{1}{2}\), 2 ⇒ x = ± \(\frac{1}{2}\), ± 2 So, there are 4 solutions. |
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67. |
Is 0.2 a root of the equation x2 - 0.4 = 0? Justify your answer. |
Answer» No, 0.2 is not a root of the equation x2 - 0.4 = 0. If we substitute the value 0.2 in place of x in the equation, x2 - 0.4 = 0 ⇒ (0.2)2 - 0.4 ≠ 0 |
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68. |
If α and β are the roots of the quadratic equation ax2 + bx + c = 0, such that β = α1/3, then(a) (a3b)1/4 + (ac3)1/4 + a = 0(b) (a3c)1/4 + (ac3)1/4 + b = 0(c) (a3b)1/4 + (ab3)1/4 + c = 0(d) (a3c)1/4 + (bc3)1/4 + a = 0 |
Answer» (b) (ac3)1/4 + (a3c)1/4 + b = 0 Let α, β be the roots of the equation ax2 + bx + c = 0. Then, α + β = \(-\frac{b}{a}\) .....(i) αβ = \(\frac{c}{a}\) ......(ii) and β = α1/3 .......(iii) ∴ From (ii) and (iii), α. (α)1/3 = \(\frac{c}{a}\) ⇒ α4/3 = \(\frac{c}{a}\) ⇒ α = \(\bigg(\frac{c}{a}\bigg)^{3/4}\) ∴ β = \(\bigg(\big(\frac{c}{a}\big)^{3/4}\bigg)^{1/3}\) = \(\bigg(\frac{c}{a}\bigg)^{1/4}\) ∴ Putting these values of a and b in eqn. (i), we have \(\bigg(\frac{c}{a}\bigg)^{3/4}\) + (c/a)1/4 = \(-\frac{b}{a}\) ⇒ a. a–3/4 c3/4 + a. a–1/4 c1/4 = – b ⇒ a1/4 c3/4 + a3/4 c1/4 + b = 0 ⇒ (ac3)1/4 + (a3c)1/4 + b = 0. |
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69. |
If α, β are the roots of ax2 + bx + c = 0, and α + k, β + k are the roots of px2 + qx + r = 0, then k =(a) \(-\frac{1}{2}\) (a/b - p/q)(b) (a/b – p/q) (c) \(\frac{1}{2}\) (b/a - q/p)(d) (ab – pq) |
Answer» (c) \(\frac{1}{2}\bigg(\frac{b}{a}-\frac{q}{p}\bigg).\) As α, β are the roots of the equation ax2 + bx + c = 0, so α + β = \(-\frac{b}{a}\), αβ = \(\frac{c}{a}\) Also, (α + x), (β + x) are the roots of the equation px2 + qx + r = 0, then α + \(x\) + β + \(x\) = – \(\frac{q}{p}\) and (α + x) (β + x) = \(\frac{r}{p}\) ⇒ α + β + 2x = – \(\frac{q}{p}\) ⇒ \(\frac{-b}{a}\) + 2x = – \(\frac{q}{p}\) ⇒ K = \(\frac{1}{2}\bigg(\frac{b}{a}-\frac{q}{p}\bigg).\) |
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70. |
If the roots of 2x2 + kx + 3 = 0 are real and equal, then the value of k is A) ± 2√6B) ± 6√2 C) ± 4 D) ± 5 |
Answer» Correct option is (A) ± 2√6 For equal roots, we have \(b^2-4ac=0\) \(\Rightarrow k^2-4\times2\times3=0\) \(\Rightarrow k^2=24\) \(\Rightarrow k=\pm\sqrt{24}\) \(=\pm\sqrt{4\times6}=\pm2\sqrt6\) Correct option is C) ± 2√6 |
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71. |
If a and b are the roots of x2 – px + q = 0, then a2 + b2 =………………… A) p2 + 2q B) p2 – q2C) p2 – 2q D) p2 + q2 |
Answer» Correct option is (C) p2 – 2q Given that a and b are roots of equation \(x^2-px + q = 0\) \(\therefore\) Sum of roots \(=\frac{-(-p)}1=p\) \(\Rightarrow\) a+b = p _____________(1) And product of roots \(=\frac q1=q\) \(\Rightarrow\) ab = q _____________(2) Now, \(a^2+b^2=(a+b)^2-2ab\) = \(p^2-2q\) Correct option is C) p2 – 2q |
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72. |
If px2 + qx + r = 0 has equal roots , then r = ……………A) q2/2pB) q/2pC) -q2/4pD) q2/4p |
Answer» Correct option is (D) q2/4p Given that quadratic equation \(Px^2+qx+r=0\) has equal roots. Then its discriminant must be zero. i.e., D = 0 \(\Rightarrow(-q)^2-4\times p\times r=0\) \(\Rightarrow q^2-4pr=0\) \(\Rightarrow4pr=q^2\) \(\Rightarrow\) \(r=\frac{q^2}{4p}\) Correct option is D) q2/4p |
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73. |
A quadratic equation in the variable x is of the form ax2 + bx + c = 0 where ………(A) a, b, c are imaginary numbers a = 0(B) a, b, c are real numbers and a ≠ 0(C) a, b, c are irrational numbers a = 0(D) a, b, c are equal numbers a ≠ 0 |
Answer» The correct answer is (B) a, b, c are real numbers and a ≠ 0. A quadratic equation in the variable x is of the form ax2 + bx + c = 0 where a, b, c are real numbers and a ≠ 0. |
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74. |
If the equation x2 + 4x + k = 0 has real and distinct roots, thenA. k < 4 B. k > 4 C. k ≥ 4 D. k ≤ 4 |
Answer» If roots of given equation are real and distinct then D = b2 – 4ac > 0 Here a = 1, b = 4 and c = k So, 42 – 4 (1) (k) >0 16 – 4k > 0 16 > 4k K< 4 |
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75. |
If the equation x2 + 4x + k = 0 has real and distinct roots, then(A) k < 4(B) k > 4(C) k ≥ 4(D) k ≤ 4 |
Answer» Answer: (A) k < 4 The given equation is x2 + 4x + k = 0 Here, a = 1, b = 4 and c = k D = b2 – 4ac = (4)2 – 4 x 1 x k = 16 – 4k The given equation will have real and distinct roots, if D > 0 16 – 4k > 0 16 > 4k 4k < 16 k < 16/4 k < 4 |
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76. |
If b = 0, c < 0, is it true the roots of x2 + bx + c = 0 are numerically equal and opposite in sign? Justify your answer. |
Answer» Yes, the roots will be equal and opposite in sign. Given, x2 + bx + c = 0, b = 0, c < 0 ⇒ x2 – c = 0 \(x = \pm \sqrt c\) Hence, the roots are equal and opposite in sign. |
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77. |
If 2x2 – 7xy + 3y2 = 0, then the value of x : y is(a) 3 : 2 (b) 2 : 3 (c) 3 : 1 and 1 : 2 (d) 5 : 6 |
Answer» (c) 3 : 1 and 1 : 2 2x2 – 7xy + 3y2 = 0 ⇒ 2\(\bigg(\frac{x}{y}\bigg)^2\) - 7\(\bigg(\frac{x}{y}\bigg)\) + 3 = 0 ∴ \(\frac{x}{y}\) = \(\frac{-b±\sqrt{b^2-4ac}}{2a}\) = \(\frac{7±\sqrt{49-24}}{4}\) = \(\frac{7±5}{4}\) = 3, \(\frac{1}{2}\) ∴ x : y = 3 : 1 and 1 : 2. |
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78. |
If b = 0, c < 0, is it true that the roots of x2 + bx + c = 0 are numerically equal and opposite in sign? Justify. |
Answer» Correct answer is Yes |
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79. |
The value of \(\sqrt{2+\sqrt{2+\sqrt{2 \,+............}}}\) is...........A) 3 B) 4C) 2 D) 8 |
Answer» Correct option is (C) 2 Let x = \(\sqrt{2+\sqrt{2+\sqrt{2\,+......}}}\) \(\Rightarrow x=\sqrt{2+x}\) \(\Rightarrow x^2=2+x\) (By squaring both sides) \(\Rightarrow x^2-x-2=0\) \(\Rightarrow x^2-2x+x-2=0\) \(\Rightarrow\) x (x - 2) + 1 (x - 2) = 0 \(\Rightarrow\) (x + 1) (x - 2) = 0 \(\Rightarrow\) x = -1 or x = 2 \(\because\) \(\sqrt{2+\sqrt{2+\sqrt{2\,+......}}}\) \(>\sqrt2>0\) \(\therefore\) \(x\neq-1\) \(\therefore\) x = 2 Hence, \(\sqrt{2+\sqrt{2+\sqrt{2\,+......}}}=2\) Correct option is C) 2 |
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80. |
The quadratic equation px2 + qx + r = 0 has imaginary roots, if ……………… A) q2 > 4 pr B) q2 < 4 pr C) q2 = 4 pr D) p = q + r |
Answer» Correct option is (B) q2 < 4 pr The quadratic equation \(px^2+qx+r=0\) has imaginary roots if \(q^2-4\,pr<0\) \(\Rightarrow\) \(q^2<4\,pr\) Correct option is B) q2 < 4 pr |
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81. |
If the sum of the squares of the roots of x2 + px – 3 = 0 is 10, then p = A) ± 2 B) ± 3 C) ± 5 D) ± 6 |
Answer» Correct option is (A) ± 2 Given quadratic equation is \(x^2+px-3=0.\) Let \(\alpha\;and\;\beta\) are roots. \(\therefore\) Sum of roots = -p \(\Rightarrow\) \(\alpha+\beta\) = -p _____________(1) And product of roots = -3 \(\therefore\) \(\alpha\beta\) = -3 _____________(2) Now, \(\alpha^2+\beta^2=10\) (Given) \(\Rightarrow\) \((\alpha+\beta)^2-2\alpha\beta=10\) \(\Rightarrow(-p)^2-2\times-3=10\) \(\Rightarrow p^2\) = 10 - 6 = 4 \(\Rightarrow\) p = \(\pm\,2\) Correct option is A) ± 2 |
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82. |
If the sum of the roots of the equation ax2 + bx + c = 0 is equal to the sum of their squares, then which one of the following is correct ?(a) a2 + b2 = c2 (b) a2 + b2 = a + b (c) 2ac = ab + b2 (d) 2c + b = 0 |
Answer» (c) ab + b2 = 2ac. Let α, β be the roots of the equation ax2 + bx + c = 0. Then, α + β = –\(\frac{b}{a}\), αβ = \(\frac{c}{a}\) Given, α + β = α2 + β2 i.e., α + β = (α2 + β)2 – 2αβ ⇒ \(\frac{-b}{a}\) = \(\frac{b^2}{a^2}\) - \(\frac{2c}{a}\) ⇒ \(-\frac{ab}{a^2}\) = \(\frac{b^2}{a^2}\) - \(\frac{2ac}{a^2}\) ⇒ ab + b2 = 2ac. |
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83. |
What is the ratio of sum of squares of roots to the product of the roots of the equation 7x2 + 12x + 18 = 0? |
Answer» Let α, β be the roots of the equation 7x2 + 12x + 18 = 0. \(\bigg[\)For a quadratic equation ax2 + bx + c = 0, sum of roots = \(-\frac{a}{b}\), product of roots = + \(\frac{c}{a}\)\(\bigg]\) ∴ α + β = \(\frac{12}{7}\) and αβ = \(\frac{18}{7}\) ⇒ (α + β)2 = \(\bigg(\frac{-12}{7}\bigg)^2\) ⇒ α2 + β2 + 2αβ = \(\frac{144}{49}\) ⇒ α2 + β2 = \(\frac{144}{49}\) - \(\frac{36}{7}\) = \(\frac{-108}{49}\) ∴ Required ratio = α2 + β2 : αβ = \(\frac{\frac{-108}{49}}{\frac{18}{7}}\) = \(-\frac{6}{7}\) = – 6 : 7. |
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84. |
Determine the nature of roots of the following quadratic equations. i. x2 – 4x + 4 = 0 ii. 2y2 – 7y + 2 = 0 iii. m2 + 2m + 9 = 0 |
Answer» i. x2 – 4x + 4= 0 Comparing the above equation with ax2 + bx + c = 0, we get a = 1, b = -4, c = 4 ∴ ∆ = b2 – 4ac = (- 4)2 – 4 × 1 × 4 = 16 – 16 ∴ ∆ = 0 ∴ Roots of the given quadratic equation are real and equal. ii. 2y2 – 7y + 2 = 0 Comparing the above equation with ay2 + by + c = 0, we get a = 2, b = -7, c = 2 ∴ ∆ = b2 – 4ac = (- 7)2 – 4 × 2 × 2 = 49 – 16 ∴ ∆ = 33 ∴ ∆ > 0 ∴ Roots of the given quadratic equation are real and unequal. iii. m2 + 2m + 9 = 0 Comparing the above equation with am2 + bm + c = 0, we get a = 1, b = 2, c = 9 ∴ ∆ = b2 – 4ac = (2)2 – 4 × 1 × 9 = 4 – 36 ∴ ∆ = -32 ∴ ∆ < 0 ∴ Roots of the given quadratic equation are not real. |
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85. |
If the equation x2 + 4x + k = 0 has real and distinct roots, then.(A) k < 4(B) k > 4(C) k ≥ 4(D) k ≤ 4 |
Answer» The correct answer is (A) k < 4. The given equation is x2 + 4x + k = 0 Here, a = 1, b = 4 and c = k D = b2 – 4ac = (4)2 – 4 x 1 x k = 16 – 4k The given equation will have real and distinct roots, if D > 0 16 – 4k > 0 16 > 4k 4k < 16 k < 16/4 k < 4 |
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86. |
Which of the following is a quadratic equation?(A) x2 - 3√x + 2 = 0(B) x + 1/x = x2(C) x2 + 1/x2 = 5(D) x2 – 5x + 3 = 0 |
Answer» Answer: (D) x2 – 5x + 3 = 0 Clearly (x2 – 5x + 3) is a quadratic polynomial. x2 – 5x + 3 = 0 is a quadratic equation. |
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87. |
If the equation x2 + 4x + k = 0 has real and distinct roots, then(A) k < 4(B) k > 4(C) k ≥ 4(D) k ≤ 4 |
Answer» Answer: (A) k < 4 The given equation is x2 + 4x + k = 0 Here, a = 1, b = 4 and c = k D = b2 – 4ac = (4)2 – 4 x 1 x k = 16 – 4k |
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88. |
If the roots of the equation ax2 + bx + c = 0 are equal in magnitude but opposite in sign, then which one of the following is correct ?(a) a = 0 (b) b = 0 (c) c = 0 (d) b = 0, c ≠ 0, a ≠ 0. |
Answer» (d) b = 0. but a ≠ 0, c ≠ 0. Given equation is ax2 + bx + c = 0. ∴Roots are x = \(\frac{-b±\sqrt{b^2-4ac}}{2a}\) Given \(\bigg[\frac{-b+\sqrt{b^2-4ac}}{2a}\bigg]\) = - \(\bigg[\frac{-b-\sqrt{b^2-4ac}}{2a}\bigg]\) ⇒ – b + \(\sqrt{b^2-4ac}\) = b + \(\sqrt{b^2-4ac}\) ⇒ 2b = 0 ⇒ b = 0. but a ≠ 0, c ≠ 0. |
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89. |
The sum of squares of the roots of x2 + 8x + 15 = 0 is …………A) 30 B) 34 C) 40 D) 44 |
Answer» Correct option is (B) 34 Given quadratic equation is \(x^2+8x+15=0\) Let roots are \(\alpha\;and\;\beta.\) \(\therefore\) Sum of roots \(=\frac{-8}1=-8\) \(\Rightarrow\) \(\alpha+\beta\) = -8 _____________(1) And product of roots \(=\frac{15}1=15\) \(\Rightarrow\) \(\alpha\beta=15\) _____________(2) Now, \((\alpha-\beta)^2=(\alpha+\beta)^2-4\alpha\beta\) \(=(-8)^2-4\times15\) = 64 - 60 = 4 \(=2^2\) \(\therefore\) \(\alpha-\beta=2\) _____________(3) By adding equations (1) & (3), we get \((\alpha+\beta)+(\alpha-\beta)=-8+2\) \(\Rightarrow\) \(2\alpha=-6\) \(\Rightarrow\) \(\alpha=\frac{-6}2=-3\) \(\therefore\) \(\beta=-8-\alpha\) (From (1)) = -8 - (-3) = -8+3 = -5 \(\therefore\) \(\alpha^2+\beta^2=(-3)^2+(-5)^2\) = 9+25 = 34 Alternative :- \(\alpha^2+\beta^2=(\alpha+\beta)^2-2\alpha\beta\) \(=(-8)^2-2\times15\) = 64 - 30 = 34 Correct option is B) 34 |
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90. |
If the roots of the quadratic equation x2 + px + 16 = 0 are equal then the value of p is A) ± 7 B) ± 6 C) ± 8 D) ± 9 |
Answer» Correct option is (C) ± 8 For equal roots, we have D = 0 \(\Rightarrow p^2-4\times1\times16=0\) \(\Rightarrow p^2=64\) \(\Rightarrow p=\pm8\) Correct option is C) ± 8 |
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91. |
If roots α, β of equation x2 -px + 16 = 0 satisfy the relation α2 + β2, then write the value of p. |
Answer» given α2 + β2 = 9 (α + β)2- 2 αβ = 9 Given x2- px + 16 = 0 and α, β are roots of the equation then Sum of roots α + β = p Product of roots α β = 16 Substituting these in (α + β)2- 2 αβ = 9 we get, p2 – 2(16) = 9 p2 = 41 P = ±√41 |
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92. |
Find the value of discriminant.i. x2 + 7x – 1 = 0ii. 2y2 – 5y + 10 = 0iii. √2 x2 + 4x + 2√2 = 0 |
Answer» i. x2 +7x – 1 = 0 Comparing the above equation with ax2 + bx + c = 0, we get a = 1, b = 7, c = -1 ∴ b2 – 4ac = (7)2 – 4 × 1 × (-1) = 49 + 4 ∴ b2 – 4ac = 53 ii. 2y2 – 5y + 10 = 0 Comparing the above equation with ay2 + by + c = 0, we get a = 2, b = -5, c = 10 ∴ b2 – 4ac = (-5)2 -4 × 2 × 10 = 25 – 80 ∴ b2 – 4ac = -55 iii. √2 x2 + 4x + 2√2 = 0 Comparing the above equation with ax + bx + c = 0, we get a = √2, b = 4, c = 2√2 ∴ b2 – 4ac = (4)2 – 4 × √2 × 2√2 = 16 – 16 ∴ b2 – 4ac = 0 |
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93. |
The value of discriminant of the quadratic equations 2x2 – 7x + 6 = 0 is(A) 1(B) -1(C) 2(D) -2 |
Answer» Answer: (A) 1 The given equation is 2x2 – 7x + 6 = 0 Here, a = 2, b = -7 and c = 6 Discriminant (D) = b2 – 4ac = (-7)2 – 4 x 2 x 6 = 49 – 48 = 1 |
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94. |
Find the discriminant of equation 2x2 – 7x + 6 = 0. |
Answer» 2x2 – 7x + 6 = 0 Compare given equation with the general form of quadratic equation, which is ax2 + bx + c = 0 Here, a = 2, b = -7 and c = 6 Discriminant formula: D = b2 – 4ac (-7)2 – 4 x 2 x 6 = 1 |
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95. |
For what value of m the ratio of the roots of the equation 12x2 – mx + 5 = 0 is 3 : 2 ?(a) 5√10 (b) 10√5 (c) 25√2 (d) 15√5 |
Answer» (a) 5\(\sqrt{10}\). Given, the roots of the given equation 12x2 – mx + 5 = 0 are in the ratio 3 : 2. Let the roots of the given equation be 3α and 2α. Then, Sum of roots = 3α + 2α = \(\frac{m}{12}\) ⇒ 5α = \(\frac{m}{12}\) ........(i) and (3α)(2α) = \(\frac{5}{12}\) ⇒ 6α2 = \(\frac{5}{12}\) ⇒ α2 = \(\frac{5}{72}\) ⇒ α = \(\sqrt{\frac{5}{12}}\) ∴ From (i) and (ii) 5. \(\sqrt{\frac{5}{12}}\) = \(\frac{m}{12}\) ⇒ m = 60\(\sqrt{\frac{5}{12}}\) = 60.\(\frac{\sqrt5}{6\sqrt2}\) = 10\(\sqrt{\frac{5}{2}}\) = 10.\(\frac{\sqrt5}{\sqrt2}\).\(\frac{\sqrt2}{\sqrt2}\) = \(\frac{10}{2}\). \(\sqrt{10}\) = 5\(\sqrt{10}\). |
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96. |
Find the zeroes of the quadratic polynomial: 3x2 + 5x + 2. |
Answer» Equating the expression with 0, 3x2 + 5x + 2 = 0 On factorising it further, 3x2 + 3x + 2x + 2 = 0 3x(x + 1) + 2(x + 1) = 0 (3x + 2) (x + 1) = 0 x = -2/3 or x = -1 The zeroes of 3x2 + 5x + 2 are – 2/3 and -1. |
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97. |
Write a quadratic polynomial, sum of whose zeros is 2√3 and their product is 2. |
Answer» The sum of the two zeros of the quadratic equation is given by \(-b/a\) Here it’s given \(-b/a\) = 2\(\sqrt{3}\) The product of the quadratic equation is \(c/a\) Here \(c/a\) = 2 the quadratic equation is of the form ax2 + b x + c = 0 or x2 + (sum of the roots) x + product of the roots = 0 \(=\text{x}^2-2\sqrt{3}\) x + 2 f(x) = k(x2 – \(2\sqrt{3}\) x + 2), where k is any real number |
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98. |
Find the zeroes of the quadratic polynomial: 2x2 - 5x + 2. |
Answer» Equating the expression with 0, 2x2 - 5x + 2 = 0 On factorising it further, 2x2 - 4x- x + 2 = 0 2x(x - 2) -1(x - 2) = 0 (2x - 1) (x - 2) = 0 x = 1/2 or x = 2 The zeroes of 2x2 - 5x + 2 are 1/2 and 2. |
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99. |
Sum of the roots of x2 – 16 = 0 isA) 1/16B) 1C) 0 D) 16 |
Answer» Correct option is (C) 0 Sum of roots of \(x^ 2-16=0\) is \(\frac{-b}a=\frac{-0}1=0\) (By comparing \(x^ 2-16=0\) with \(ax^2+bx+c=0,\) we get a = 1, b = 0, c = -16) Correct option is C) 0 |
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100. |
Find the Discriminant of quadratic equations (i) 2x2 - 7x + 6 = 0(ii) 3x2 - 2x + 8 = 0(iii) 2x2 - 5\(\sqrt{2x}\) + 4 = 0 |
Answer» (i) 2x2 - 7x + 6 = 0 Here a = 2 b = - 7 c = 6 Discriminant D is diven by: D = b2 - 4ac = (-7)2 - 4 x 2 x 6 = 49 - 48 = 1 (ii) 3x2 - 2x + 8 = 0 Here a = 3, b = -2, c = 8 Discriminant D is given by: D = b2 - 4ac = (-2)2 - 4 x 3 x 8 = 4 - 96 = - 92 (iii) 2x2 - 5\(\sqrt{2x}\) + 4 = 0 Here a = 2 b = - 5√2. c = 4 Discriminant D is given by: D = b2 - 4ac = (- 5√2)2 - 4 x 2 x 4 = (25 x 2) - 32 = 50 - 32 = 18 |
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