Question
Prove the following results:
$2\sin^{-1}\frac{3}{5}=\tan^{-1}\frac{24}{7}$

Answer

$2\sin^{-1}\frac{3}{5}=\tan^{-1}\frac{24}{7}$ $\text{L.H.S}=2\sin^{-1}\frac{3}{5}$ $=2\times\tan^{-1}\begin{bmatrix}\frac{\frac{3}{5}}{\sqrt{1-\Big(\frac{3}{5}\Big)^2}}\end{bmatrix}$ $\bigg\{\text{Since }\sin^{-1}\text{x}=\tan^{-1}\frac{\text{x}}{\sqrt{1-\text{x}^2}}\bigg\}$ $=2\tan^{-1}\Bigg(\frac{\frac{3}{5}}{\frac{4}{5}}\Bigg)$ $=2\tan^{-1}\Big(\frac{3}{4}\Big)$ $=\tan^{-1}\Bigg(\frac{2\times\frac{3}{4}}{1-\big(\frac{3}{4}\big)^2}\Bigg)$ $\Big\{\text{Since }2\tan^{-1}\text{x}=\tan^{-1}\frac{2\text{x}}{1-\text{x}^2}\Big\}$ $=\tan^{-1}\bigg(\frac{\frac{3}{2}}{\frac{7}{16}}\bigg)$ $=\tan^{-1}\Big(\frac{24}{7}\Big)$ $=\text{R.H.S}$So,
$2\sin^{-1}\frac{3}{5}=\tan^{-1}\frac{24}{7}$

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