(sin5π/12-sinπ/12)(cos5π/12+cosπ/12)=?
问题描述：
(sin5π/12-sinπ/12)(cos5π/12+cosπ/12)=?
答
(sin5π/12-sinπ/12)(cos5π/12+cosπ/12)
=(cosπ/12 - sinπ/12)(sinπ/12 + cosπ/12)
=cos²(π/12) - sin²(π/12)
=cos(π/6)
=(根号3)/2(sin5π/12-sinπ/12)(cos5π/12+cosπ/12)怎么会变成（cosπ/12 - sinπ/12)(sinπ/12 + cosπ/12）公式：sin(π/2 - α)=cosα，cos(π/2 - α)=sinα