sin18°sin54°=?用公式算不要用计算器
问题描述：
sin18°sin54°=?用公式算不要用计算器
答
sin18°sin54°
= sin18°sin54°*cos18°/cos18°
=（1/2sin36°sin54°）/cos18°
=（1/2sin36°cos36°）/cos18°
=（1/4sin72°）/cos18°
=（1/4cos18°）/cos18°
=1/4
答
好厉害啊，我这题纠结了好久
答
其实就是配一下
= 4sin18°sin54°*cos18°/4cos18°
=（2sin36°sin54°）/4cos18°
=（2sin36°cos36°）/4cos18°
=2sin72°/4cos18°
=cos18°/4cos18°
=1/4