sin18°cos12°+cos18°cos78°
问题描述:
sin18°cos12°+cos18°cos78°
答
sin18°cos12°+cos18°sin12°=sin(18°+12°)=sin30°=1/2
sin18°cos12°+cos18°cos78°
sin18°cos12°+cos18°sin12°=sin(18°+12°)=sin30°=1/2