cos1/2a,π表1100

(cos 1(sin 1(cos1 sin 1.
a是第二象限角,sina cosa等于三分之根号三,求cos2a等于多少?
cosa2-1记:二余弦二提前方余弦把一减3,tg2a=2tga(1-tana平方)分子是
tan(π/4 a=1/2 求(sin2a-cos平方a(1 cos2a)
7π8-cos π8 根据倍角公式cos 2a 2(cos a^2 1