যোজিত ফল নির্ণয় কর:    $\int \frac{a dx}{\left ( \left ( \sqrt{x^{2} + a^{2}} \right )^{3} \right.}$  

$\begin{array}{l} \int \frac{\mathrm{adx}}{\left(\sqrt{\mathrm{x}^{2}+\mathrm{a}^{2}}\right)^{3}} ; \text { let, } \mathrm{x}=\mathrm{a} \tan \theta \therefore \mathrm{dx}=\mathrm{a} \mathrm{sec}^{2} \theta \mathrm{d} \theta \\ =\int \frac{\mathrm{a}^{2} \sec ^{2} \theta \mathrm{d} \theta}{\left\{\mathrm{a}^{2}\left(1+\tan ^{2} \theta\right)\right\}^{3 / 2}}=\int \frac{\mathrm{a}^{2} \sec ^{2} \theta \mathrm{d} \theta}{\mathrm{a}^{3} \sec ^{3} \theta}=\frac{1}{\mathrm{a}} \int \cos \theta \mathrm{d} \theta=\frac{1}{\mathrm{a}} \sin \theta+\mathrm{c}=\frac{1}{\mathrm{a}} \sin \left[\tan ^{-1}\left(\frac{\mathrm{x}}{\mathrm{a}}\right)\right]+\mathrm{c} \text { [Ans.] }\end{array}$