如题所述
求完整步骤~~
a=x+y0 ≤x ≤pai0 ≤y ≤2pai0 ≤x+y ≤3pai0 ≤a≤3pai对于sin(a)在0 ≤a≤3pai内分区如下0≤a<pai,Isin(a)I=sin(a)pai≤a<2pai,Isin(a)I=-sin(a)2pai≤a≤3pai,Isin(a)I=sin(a)剩下就是积分了