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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Quadratic Equation

NDA 2025 · Mathematics · Quadratic Equation

For the following two (02) items: Let α and β be the roots of the...

For the following two (02) items:
Let α\alpha and β\beta be the roots of the quadratic equation x2+(log⁡0.5(a2))x+(log⁡0.5(a2))4=0x^2 + (\log_{0.5}(a^2))x + (\log_{0.5}(a^2))^4 = 0, where a2≠1a^2 \neq 1 and log⁡0.5(a2)>0\log_{0.5}(a^2) > 0. Further, β2=α(log⁡a2(0.5))\beta^2 = \alpha(\log_{a^2}(0.5)).

What is the relation between α\alpha and β\beta?

Options

  1. Aα=2β\alpha = 2\beta
  2. B2α=β2\alpha = \beta
  3. Cα=−2β\alpha = -2\beta
  4. D2α=−β2\alpha = -\beta

Correct answer

C. α=−2β\alpha = -2\beta

Step-by-step solution

Let p=log⁡0.5(a2)p = \log_{0.5}(a^2). We are given p>0p > 0.

The given quadratic equation is:
x2+px+p4=0x^2 + px + p^4 = 0

Let the roots be α\alpha and β\beta. Then:
α+β=−p\alpha + \beta = -p
αβ=p4\alpha \beta = p^4

We are given the relation:
β2=αlog⁡a2(0.5)\beta^2 = \alpha \log_{a^2}(0.5)

Using the change of base formula, log⁡a2(0.5)=1log⁡0.5(a2)=1p\log_{a^2}(0.5) = \dfrac{1}{\log_{0.5}(a^2)} = \dfrac{1}{p}.
Thus, the relation becomes:
β2=αp  ⟹  α=pβ2\beta^2 = \dfrac{\alpha}{p} \implies \alpha = p\beta^2

Substitute α=pβ2\alpha = p\beta^2 into the product of roots:
(pβ2)(β)=p4  ⟹  pβ3=p4(p\beta^2)(\beta) = p^4 \implies p\beta^3 = p^4

Since p>0p > 0, we can divide by pp to get:
β3=p3\beta^3 = p^3

Assuming β\beta is a real root, we have β=p\beta = p.
Substitute β=p\beta = p into the sum of roots:
α+p=−p  ⟹  α=−2p\alpha + p = -p \implies \alpha = -2p

Now we can find the relation between α\alpha and β\beta:
α=−2p=−2β\alpha = -2p = -2\beta

Thus, α=−2β\alpha = -2\beta.

Answer: α=−2β\alpha = -2\beta
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