Find the derivative of f(x)=arctan(sinhx)f(x) = \arctan(\sinh x)f(x)=arctan(sinhx).
sech(x)\text{sech}(x)sech(x)
1coshx\frac{1}{\cosh x}coshx1
sech2(x)\text{sech}^2(x)sech2(x)
tanh(x)\tanh(x)tanh(x)