sinnπx/D*sinnπx/d
=(1/2)[cos(nπx/D-nπx/d)-cos(nπx/D+nπx/d)]
=(1/2)[cos(d-D)nπx/Dd-cos(d+D)nπx/Dd]
对0到d积分得
(1/2){[Dd/(d-D)nπ]sin(d-D)nπx/Dd-[Dd/(d+D)nπ]sin(d+D)nπx/Dd}|d 0【这里电脑不能打成竖排自己写成那个格式吧】
=(1/2){[Dd/(d-D)nπ]sin(d-D)nπ/D-[Dd/(d+D)nπ]sin(d+D)nπ/D}-0
=(1/2){[Dd/(d-D)nπ]sin(d-D)nπ/D-[Dd/(d+D)nπ]sin(d+D)nπ/D}