cos方5π/12+cos方π/12+cosπ/12*cos5π/12 最后等于4/5的过程.
问题描述：
cos方5π/12+cos方π/12+cosπ/12*cos5π/12 最后等于4/5的过程.
答
cos^2(π/4+π/6)+cos^2(π/4-π/6)+1/2[cos(5π/12+π/12)+cos(5π/12-π/12)]=cos^2(π/4+π/6)+cos^2(π/4-π/6)+1/2[cos(π/2)+cosπ/3]=2cos^2(π/4)cos^2(π/6)+2sin^2(π/4)sin^2(π/6)+1/4=2*1/2*3/4+2*1/2*...