MCQ
$\begin{aligned}3\left[\sin^4\left(\frac{3\pi}{2}-\alpha\right)+\right.&\left.\sin^4(3\pi+\alpha)\right]-2\left[\sin^6\left(\frac{\pi}{2}+\alpha\right)+\sin^6(5\pi-\alpha)\right]=\end{aligned}$
  • A
    $0$
  • 1
  • C
    3
  • D
    $\sin4\alpha+\sin6\alpha$

Answer

Correct option: B.
1
(B)
$3\left\{\sin^4\left(\frac{3\pi}{2}-\alpha\right)+\sin^4(3\pi+\alpha)\right\}$
$-2\left\{\sin^6\left(\frac{\pi}{2}+\alpha\right)+\sin^6(5\pi-\alpha)\right\}$
$=3\left\{(-\cos\alpha)^4+(-\sin\alpha)^4\right\}-2\left(\cos^6\alpha+\sin^6\alpha\right)$
$=3\left(1-2\sin^2\alpha\cos^2\alpha\right)-2\left(1-3\sin^2\alpha\cos^2\alpha\right)$
$=3-6\sin^2\alpha\cos^2\alpha-2+6\sin^2\alpha\cos^2\alpha$
$=3-2=1$

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