cos方5π/12+cos方π/12+cosπ/12*cos5π/12 最后等于5/4的过程.
问题描述：
cos方5π/12+cos方π/12+cosπ/12*cos5π/12 最后等于5/4的过程.
答
cos²5π/12+cos²π/12+cosπ/12*cos5π/12
由于cos5π/12=sin（π/2-5π/12）=sinπ/12
原式=sin²π/12+cos²π/12+cosπ/12sinπ/12
=1+½sinπ/6
=1+1/4
=5/4