sin(18°)sin(54°)
问题描述：
sin(18°)sin(54°)
sin(18°)*sin(54°) 不用计算器
答
cos36*cos72
=cos36*sin18
=(1/cos18)*sin18*cos18*cos36
=(1/2cos18)*sin36*cos36
=(1/4cos18)*sin72
=1/4