The derivative of sech(x) is -sech(x)tanh(x). This can be derived using the chain rule and the derivative of sech(x) = -sech(x)tanh(x). Alternatively, it can be obtained using the identity sech^2(x) + tanh^2(x) = 1, which implies that the derivative of sech^2(x) is -2sech(x)tanh(x).
