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WBJEE · Maths · Complex Number

If \(z=x\) - iy and \(z^{1 / 3}=p+\) iq \((x, y, p, q \in \mathbb{R})\), then \(\frac{\left(\frac{x}{p}+\frac{y}{q}\right)}{\left(p^2+q^2\right)}\) is equal to

  1. A 2
  2. B -1
  3. C 1
  4. D \(-2\)
Verified Solution

Answer & Solution

Correct Answer

(D) \(-2\)

Step-by-step Solution

Detailed explanation

\(z=p^3-3 p q^2+i\left(3 p^2 q-q^3\right)=x-i y\) \(\begin{aligned} &x=p\left(p^2-3 q^2\right) \\ &y=-q\left(3 p^2-q^2\right) \\ &\therefore \frac{x}{p}+\frac{y}{q}=p^2-3 q^2-3 p^2+q^2=-2\left(p^2+q^2\right) \end{aligned}\)