exp (x)/(1+exp (2*x))

solve(exp(x)/(exp(2*x) + 1), x)

diff(exp(x)/(exp(2*x) + 1), x)

series(exp(x)/(exp(2*x) + 1), x, 0, 10)

Want to compute something more complicated? Try a full Python/SymPy console at SymPy Live.