Question 26

Mathematics Linear and Quadratic Equations Easy

Given below are two statements:

Statement I: If the roots of the quadratic equation \( x^{2}-4 x- \) \( \log _{3} a=0 \) are real, then the least value of \( a \) is \( 1 / 81 \) .
Statement II: The harmonic mean of the roots of the equations \( (5+\sqrt{2}) x^{2}-(4+\sqrt{5}) x+(8+2 \sqrt{5})=0 \) is 2
In the light of the above statements, choose the correct answer from the options given below:

(A) Both Statement 1 and Statement II are true
(B) Both Statement I and Statement II are false
(C) Statement I is true but Statement II is false
(D) Statement 1 is false but Statement II is true
✓ Correct Answer: Option C Verified Solution

📘 Step-by-Step Solution & Detailed Explanation:

Statement I: Given the quadratic equation: \[ x^2 - 4x - \log_3 a = 0 \] For the roots to be real, the discriminant must be non-negative: \[ \Delta = b^2 - 4ac \geq 0 \] Here, \( a = 1 \), \( b = -4 \), and \( c = -\log_3 a \). So, \[ (-4)^2 - 4(1)(-\log_3 a) \geq 0 \] \[ 16 + 4\log_3 a \geq 0 \] \[ 4\log_3 a \geq -16 \] \[ \log_3 a \geq -4 \] \[ a \geq 3^{-4} \] \[ a \geq \frac{1}{81} \] Thus, the least value of \( a \) is \( \frac{1}{81} \). Statement I is true. Statement II: Given the quadratic equation: \[ (5 + \sqrt{2})x^2 - (4 + \sqrt{5})x + (8 + 2\sqrt{5}) = 0 \] Let the roots be \( \alpha \) and \( \beta \). The harmonic mean (HM) of the roots is given by: \[ \text{HM} = \frac{2\alpha\beta}{\alpha + \beta} \] From the quadratic equation: \[ \alpha + \beta = \frac{4 + \sqrt{5}}{5 + \sqrt{2}} \] \[ \alpha\beta = \frac{8 + 2\sqrt{5}}{5 + \sqrt{2}} \] Calculating the harmonic mean: \[ \text{HM} = \frac{2 \cdot \frac{8 + 2\sqrt{5}}{5 + \sqrt{2}}}{\frac{4 + \sqrt{5}}{5 + \sqrt{2}}} = \frac{2(8 + 2\sqrt{5})}{4 + \sqrt{5}} \] Simplifying: \[ \text{HM} = \frac{16 + 4\sqrt{5}}{4 + \sqrt{5}} = 4 \] The statement claims the harmonic mean is 2, but our calculation shows it is 4. Statement II is false. Conclusion: - Statement I is true. - Statement II is false. Therefore, both statements are not correct. The correct answer is: C. Statement I is true but Statement II is false

Practice Similar Linear and Quadratic Equations Questions

Reinforce your conceptual grasp with related questions from CUET-MCA 2023:

Q67 Given below are two statements: One is labelled as Assertion A and the...
Solve →
Q84 Let \( a=cos 2 π/7+i sin 2 π/7, α=a+a 2 +a 4 \) and \( β=a 3 +a 5 +a 6 \)...
Solve →
Q94 If every pair from among the equation \( x 2 +p x+q r=0, x 2 + \) \( q x+r...
Solve →
Q14 The area of a rhombus is \( 120 ~cm 2 \) and length of its one diagonal in...
Solve →
Q24 If \( cot 2 45 -sin 2 45 =K sin 2 30 × tan 2 45 × sec 2 45 \) , then the...
Solve →
Full-Length Test Series

Prepare for CUET-MCA Under Real Exam Conditions

Take timed full-length mock tests with authentic question distributions, negative marking (+12/-3 in Math), and instant All India Rank calculation.

Start Free Mock Test Series →