cos^2 5π/12-sin^2 7π/12=? 求详细过程

题目

cos^2 5π/12-sin^2 7π/12=? 求详细过程

答案

con²(5π/12)-sin²(7π/12)=cos²(5π/12)-sin²(π-7π/12)=cos²(5π/12)-sin²(5π/12)=cos(2*5π/12)=cos(5π/6)=-(√3)/2