MCQ
If $\sin ^{-1} \frac{1}{3}+\sin ^{-1} \frac{2}{3}=\sin ^{-1} x$, then $x$ is equal to
  • A
    $0$
  • B
    $\frac{\sqrt{5}-4 \sqrt{2}}{9}$
  • $\frac{\sqrt{5}+4 \sqrt{2}}{9}$
  • D
    $\frac{\pi}{2}$

Answer

Correct option: C.
$\frac{\sqrt{5}+4 \sqrt{2}}{9}$
(C) $\sin ^{-1} \frac{1}{3}+\sin ^{-1} \frac{2}{3}$
$=\sin ^{-1}\left[\frac{1}{3} \sqrt{1-\frac{4}{9}}+\frac{2}{3} \sqrt{1-\frac{1}{9}}\right]$
$=\sin ^{-1}\left[\frac{\sqrt{5}+4 \sqrt{2}}{9}\right]$
$\therefore \quad x=\frac{\sqrt{5}+4 \sqrt{2}}{9}$

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