例3计算 cos xdx. 解令t=cosx,l=- sin xd, T →t=0.x=0→t=1 20 cosxsin xdx rrdtszgr 0cos sin . 2 0 5   x xdx 解 令 t = cos x, dt = −sin xdx, 2  x = t = 0, x = 0  t = 1,   2 0 5 cos x sin xdx = − 0 1 5 t dt 1 0 6 6 t = . 6 1 = 例3 计算