TITLE: Is there a formula for the area under $\tanh(x)$?
QUESTION [7 upvotes]: I understand trigonometry but I've never used hyperbolic functions before.

Is there a formula for the area under $\tanh(x)$?

I've looked on Wikipedia and Wolfram but they don't say if there's a formula or not.
I tried to work it out myself and I got this far:
$\tanh(x) = {\sinh(x)\over\cosh(x)} = {1-e^{-2x}\over 1+e^{-2x}} = {e^{2x}-1\over e^{2x}+1} = {e^{2x}+1-2\over e^{2x}+1} = 1-{2\over e^{2x}+1}$
Now I'm stuck. I don't know if I'm on the right track or not.

REPLY [3 votes]: Why all those difficult substitutions and jabbers? 
Just observe that we can use the logarithm derivative formula:
$$\int\frac{f'(x)}{f(x)}\ \text{d} x = \ln(f(x)) + C$$
thence, having $\tanh(x) = \frac{\sinh(x)}{\cosh(x)} = \frac{f'(x)}{f(x)}$ it comes easy to get the result
$$\int\frac{\sinh(x)}{\cosh(x)}\ \text{d}x = \ln(\cosh(x)) + C$$