证明sin^2(a
证明sin^2(a-60)+sin^2a+sin^2(60+a)=1.5
证明sin^2(a-60)+sin^2a+sin^2(60+a)=1.5 证明 2[sin^2(a-60)+sin^2a+sin^2(60+a)] =3-cos(2a-120)-cos2a-cos(120+2a) =3-2cos(2a)*cos(120)-cos(2a) =3+cos(2a)-cos(2a)=3