(2)の不定積分
∫e^x*sin(kπx)dx = e^x*sin(kπx)- kπ∫e^x*cos(kπx)dx
∫e^x*cos(kπx)dx = e^x*cos(kπx) + kπ∫e^x*sin(kπx)dxなので
∫e^x*sin(kπx)dx = e^x*sin(kπx) - kπ( e^x*cos(kπx) + kπ∫e^x*sin(kπx)dx )
(1+k^2*π^2)∫e^x*sin(kπx)dx = e^x*sin(kπx) - kπe^x*cos(kπx)
∫e^x*sin(kπx)dx = (e^x*sin(kπx) - kπe^x*cos(kπx))/ (1+k^2*π^2)