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NDA 2026
Exam
NDA
Year
2026
Subject
Mathematics
Chapter
Complex Number

NDA 2026 · Mathematics · Complex Number

If α , β , γ are cube roots of -8 , then what is (α^2 p^2+β^2...

If α\alpha, β\beta, γ\gamma are cube roots of −8-8, then what is α2p2+β2q2+γ2r2β2p2+γ2q2+α2r2\dfrac{\alpha^2 p^2+\beta^2 q^2+\gamma^2 r^2}{\beta^2 p^2+\gamma^2 q^2+\alpha^2 r^2} equal to ?

Options

  1. Aγα\dfrac{\gamma}{\alpha}
  2. Bγβ\dfrac{\gamma}{\beta}
  3. C2γα\dfrac{2\gamma}{\alpha}
  4. D2γβ\dfrac{2\gamma}{\beta}

Correct answer

B. γβ\dfrac{\gamma}{\beta}

Step-by-step solution

Since α,β,γ\alpha, \beta, \gamma are the cube roots of −8-8, they are the roots of the equation z3+8=0z^3 + 8 = 0.

Thus, we have α3=β3=γ3=−8\alpha^3 = \beta^3 = \gamma^3 = -8.

The product of the roots of the cubic equation z3+8=0z^3 + 8 = 0 is given by αβγ=−8\alpha \beta \gamma = -8.

Using these properties, we can find relations between the roots:

α3=αβγ⇒α2=βγ\alpha^3 = \alpha \beta \gamma \Rightarrow \alpha^2 = \beta \gamma

β3=αβγ⇒β2=αγ\beta^3 = \alpha \beta \gamma \Rightarrow \beta^2 = \alpha \gamma

γ3=αβγ⇒γ2=αβ\gamma^3 = \alpha \beta \gamma \Rightarrow \gamma^2 = \alpha \beta

Let the given expression be E=α2p2+β2q2+γ2r2β2p2+γ2q2+α2r2E = \dfrac{\alpha^2 p^2+\beta^2 q^2+\gamma^2 r^2}{\beta^2 p^2+\gamma^2 q^2+\alpha^2 r^2}.

Consider multiplying the denominator by the fraction γβ\dfrac{\gamma}{\beta}:

γβ(β2p2+γ2q2+α2r2)=βγp2+γ3βq2+α2γβr2\dfrac{\gamma}{\beta} (\beta^2 p^2 + \gamma^2 q^2 + \alpha^2 r^2) = \beta \gamma p^2 + \dfrac{\gamma^3}{\beta} q^2 + \dfrac{\alpha^2 \gamma}{\beta} r^2

Now, substitute the derived relations into each term of this expansion:

For the first term, substitute βγ=α2\beta \gamma = \alpha^2 to get α2p2\alpha^2 p^2.

For the second term, since γ3=β3=−8\gamma^3 = \beta^3 = -8, we have γ3β=β3β=β2\dfrac{\gamma^3}{\beta} = \dfrac{\beta^3}{\beta} = \beta^2, which gives β2q2\beta^2 q^2.

For the third term, substitute α2=βγ\alpha^2 = \beta \gamma to get (βγ)γβr2=γ2r2\dfrac{(\beta \gamma) \gamma}{\beta} r^2 = \gamma^2 r^2.

Adding these terms together, we get:

γβ(β2p2+γ2q2+α2r2)=α2p2+β2q2+γ2r2\dfrac{\gamma}{\beta} (\beta^2 p^2 + \gamma^2 q^2 + \alpha^2 r^2) = \alpha^2 p^2 + \beta^2 q^2 + \gamma^2 r^2

This shows that the numerator is exactly γβ\dfrac{\gamma}{\beta} times the denominator.

Therefore, the value of the given expression is γβ\dfrac{\gamma}{\beta}.

Answer: γβ\dfrac{\gamma}{\beta}
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