Question

cosa方+cos(60度-a)方+cos(60度+a)方谢谢了

Answer 1

cos^2(a)+cos^2(60-a)+cos^2(60+a)

=cos^2(a)+[1/2*cos(a)+√3/2*sin(a)]^2+[1/2*cos(a)-√3/2*sin(a)]^2

=cos^2(a)+[1/4*cos^2(a)+3/4*sin^2(a)]*2

=3/2*cos^2(a)+3/2*sin^2(a)

=3/2