https://s0.wp.com/latex.php?latex=f%28x%29+%3D+tanh%28x%29+%3D+%5Cfrac%7B%5Cexp%28x%29+-+%5Cexp%28-x%29%7D%7B%5Cexp%28x%29+%2B+%5Cexp%28x%29%7D&bg=eeeeee&fg=666666&s=0&c=20201002