2倍角公式

题目

2倍角公式
求值》
cosπ/12 x cos5π/12

答案

cosπ/12 x cos5π/12
=1/2(cos(π/12+5π/12)+cos(π/12-5π/12))
=1/2(cos(π/2+cos(-π/3))
=1/2cosπ/3
=1/2*1/2=1/4