cos(a b)推导过程,

化简cos(a-b)cos(a-y-sin(a-b)sin(y-a)
已知cos(a b)等于0,sinb等于三分之二,求sin(2a 3b)
数学:求证:锐角三角形中(cosa cosb cosc3≤cos(a b c3)
cos^2(a-b-cos^2(a b=1/2(1 cos2a(1 cos2b=1/3
答:sin(b c=sin(180-a=sin180°cosa-sinacos180°其中sin180=0