$\int \frac{1}{e^{a x}+e^{-a x}} d x=?$

$\frac{1}{a} \cot ^{-1}\left(e^{a x}\right)+C$

$\frac{1}{a} \tan ^{-1}\left(e^{a x}\right)+C$

$\frac{1}{a} \tan ^{-1}\left(1+e^{a x}\right)+C$

$\frac{1}{a} \cot ^{-1}\left(1+e^{a x}\right)+C$