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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Quadratic Equation

NDA 2025 · Mathematics · Quadratic Equation

If one root of the equation x^2 - kx + k = 0 exceeds the other by 2...

If one root of the equation x2−kx+k=0x^2 - kx + k = 0 exceeds the other by 232\sqrt{3}, then which one of the following is a value of kk?

Options

  1. A33
  2. B66
  3. C99
  4. D1212

Correct answer

B. 66

Step-by-step solution

Let the roots of the equation x2−kx+k=0x^2 - kx + k = 0 be α\alpha and β\beta.

Given that one root exceeds the other by 232\sqrt{3}, we have ∣α−β∣=23|\alpha - \beta| = 2\sqrt{3}.

Squaring both sides, we get (α−β)2=12(\alpha - \beta)^2 = 12.

Using the identity (α−β)2=(α+β)2−4αβ(\alpha - \beta)^2 = (\alpha + \beta)^2 - 4\alpha\beta, we can substitute the sum and product of the roots.

From the given quadratic equation, α+β=k\alpha + \beta = k and αβ=k\alpha\beta = k.

Substituting these values, we get k2−4k=12k^2 - 4k = 12.

k2−4k−12=0k^2 - 4k - 12 = 0

(k−6)(k+2)=0(k - 6)(k + 2) = 0

Thus, k=6k = 6 or k=−2k = -2.

Among the given options, 66 is a value of kk.

Answer: 66
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