Practicing Success
$\int \frac{d x}{5+4 \cos x}$ is equal to : |
$\frac{2}{3} \tan ^{-1}\left(\frac{1}{3} \tan \frac{x}{2}\right)+c$ $-\frac{2}{3} \tan ^{-1}\left(\frac{1}{3} \tan \frac{x}{2}\right)+c$ $\frac{1}{3} \tan ^{-1}\left(\frac{1}{3} \tan \frac{x}{2}\right)+c$ None of these |
$\frac{2}{3} \tan ^{-1}\left(\frac{1}{3} \tan \frac{x}{2}\right)+c$ |
Let $I=\int \frac{d x}{5+4 \cos x}$ Let $t=\tan \frac{x}{2} \Rightarrow dx=\frac{2 d t}{1+t^2}$ $\Rightarrow I=\int \frac{\frac{2 d t}{1+t^2}}{5+4\left(\frac{1-t^2}{1+t^2}\right)}=2 \int \frac{d t}{t^2+9}$ $=2 . \frac{1}{3} . \tan ^{-1}\left(\frac{t}{3}\right)+c$ $\Rightarrow I=\frac{2}{3} \tan ^{-1}\left(\frac{1}{3} \tan \frac{x}{2}\right)+c$ Hence (1) is the correct answer. |