如果 g(x) = e^h(x), 则 g'(x) = h'(x)e^h(x) 所以 f(x)=e^-kx+(x^2+x-1/k) f '(x) = [d(-kx)/dx]*e^(-kx) + 2x + 1 = -ke^(-kx) + 2x + 1
