cos^2(π/2-a)+cos2^2(π/6+a)
=sin^2a+1/2(1+cos(π/3+2a)
=1/2(1-cos(π/3+2a)+1/2(1+cos(π/3+2a)
=1cos^2(3/π-a)+cos^2(6/π+a)= =我题目写错了cos^2(3/π-a)+cos^2(6/π+a)=1/2{1+cos(2π/3-2a)}+1/2{cos(π/3+2a)}=1/2+1/2cos(π-π/3-2a)+1/2+1/2(cos(π/3+2a)=1-1/2cos(π/3+2a)+1/2(cos(π/3+2a)=1