Q50 / 160 · AP EAMCET 2018 (22 Apr Shift 1) · Mathematics

If $1, \omega, \omega^2$ are the cube roots of unity, then $\frac{1}{1+2 \omega}+\frac{1}{2+\omega}-\frac{1}{1+\omega}=$

  • A
    1
  • B
    $\omega$
  • C
    $\omega^2$
  • Correct answer
    D
    0

Solution

$$ \begin{aligned} & \text { Given, } \frac{1}{1+2 \omega}+\frac{1}{2+\omega}-\frac{1}{1+\omega} \\ & =\frac{2+\omega+1+2 \omega}{(1+2 \omega)(2+\omega)}-\frac{1}{(1+\omega)} \\ & =\frac{3+3 \omega}{(1+2 \omega)(2+\omega)}-\frac{1}{(1+\omega)} \\ & =\frac{(3+3 \omega)(1+\omega)-(1+2 \omega)(2+\omega)}{(1+2 \omega)(2+\omega)(1+\omega)} \\ & =\frac{3+3 \omega+3 \omega+3 \omega^2-\left(2+\omega+4 \omega+2 \omega^2\right)}{(1+2 \omega)(2+\omega)(1+\omega)} \\ & =\frac{3+6 \omega+3 \omega^2-2-w-4 \omega-2 \omega^2}{(1+2 \omega)(2+\omega)(1+\omega)} \\ & =\frac{1+\omega+\omega^2}{(1+2 \omega)(2+\omega)(1+\omega)} \\ & =0 \end{aligned} $$

Hence, the correct answer is option: 'D'.

Relevant Questions