空谷幽
幼苗
共回答了9个问题 举报
参考例题:
化简 coa^ 2a+cos^2 (a+π/3)-cosa cos(a+π/3)
coa^ 2a+cos^2 (a+π/3)-cosa cos(a+π/3)
=(cosa)^2-cos(π/3+a)[cosa-cos(π/3+a)]
=(cosa)^2-cos(π/3+a)sin(π/6+a)
=(cosa)^2-1/2*[sin(2a+π/2)-1/2]
=(cosa)^2-1/2*cos2a+1/4
=(cosa)^2-1/2*[2(cosa)^2-1]+1/4
=3/4.
1年前
0