2/3sina^2+(1/4cosa^2)=?
问题描述：
2/3sina^2+(1/4cosa^2)=?
答
原式=5/12*sin²a+1/4*(sin²a+cos²a)
=5/12*(1-cos2a)/2+1/4*1
=5/12-5/24*cos2a+1/4
=2/3-5/24*cos2a答案是7/12sincos在哪里啊