MCQ
$\sin \left(3 \sin ^{-1}\left(\frac{2}{5}\right)\right)=$
  • $\frac{118}{125}$
  • B
    $\frac{115}{127}$
  • C
    $\frac{128}{135}$
  • D
    $\frac{110}{118}$

Answer

Correct option: A.
$\frac{118}{125}$
(A) $\sin \left(3 \sin ^{-1}\left(\frac{2}{5}\right)\right)=\sin 3 \theta$,
Where $\theta=\sin ^{-1}\left(\frac{2}{5}\right) \ldots\left[\theta=\sin ^{-1}\left(\frac{2}{5}\right), \sin \theta=\frac{2}{5}\right]$
$=3 \sin \theta-4 \sin ^3 \theta$
$=3\left(\frac{2}{5}\right)-4\left(\frac{2}{5}\right)^3 \ldots\left[\theta=\sin ^{-1}\left(\frac{2}{5}\right), \sin \theta=\frac{2}{5}\right]$
$=\frac{6}{5}-\frac{32}{125}=\frac{118}{125}$

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