If $\omega$ is complex cube root of unity and $(1+\omega)^7=\mathrm{A}+\mathrm{B} \omega$, then values of A…

If $\omega$ is complex cube root of unity and $(1+\omega)^7=\mathrm{A}+\mathrm{B} \omega$, then values of A and B are, respectively.
  1. 0,1
  2. 1,0
  3. 1,1
  4. $-1,1$

Solution

$\begin{aligned} & (1+\omega)^7=\mathrm{A}+\mathrm{B} \omega \\ & \therefore \mathrm{A}+\mathrm{B} \omega=\left(-\omega^2\right)^7 \quad \ldots\left(\because 1+\omega+\omega^2=0\right] \\ & =(-1) \omega^{14}=-\omega^{12} \omega^2=-\omega^2=(1+\omega) \\ & \therefore A=1, B=1\end{aligned}$

Asked in: MHT CET 2021 (20 Sep Shift 2)

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