MCQ
If $\cot ^{-1} \frac{3}{4}+\sin ^{-1} \frac{5}{13}=\sin ^{-1}(k)$, then $k=$
  • $\frac{63}{65}$
  • B
    $\frac{12}{13}$
  • C
    $\frac{65}{68}$
  • D
    $\frac{5}{12}$

Answer

Correct option: A.
$\frac{63}{65}$
(a) : Let $\cot ^{-1} \frac{3}{4}=\theta \Rightarrow \cot \theta=\frac{3}{4}$ and $\sin \theta=\frac{1}{\sqrt{1+\cot ^2 \theta}}=\frac{1}{\sqrt{1+(9 / 16)}}=\frac{4}{5}$ Hence, $\cot ^{-1} \frac{3}{4}+\sin ^{-1} \frac{5}{13}=\sin ^{-1} \frac{4}{5}+\sin ^{-1} \frac{5}{13}$ $=\sin ^{-1}\left[\frac{4}{5} \cdot \sqrt{1-\frac{25}{169}}+\frac{5}{13} \cdot \sqrt{1-\frac{16}{25}}\right]$ $=\sin ^{-1} \frac{63}{65}$

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