三角函数题:cos(36度)*cos(72度)=
问题描述:
三角函数题:cos(36度)*cos(72度)=
答
cos36*cos72
=cos36*sin18
=(1/cos18)*sin18*cos18*cos36
=(1/2cos18)*sin36*cos36
=(1/4cos18)*sin72
=1/4