cos(a+b)推导,cos(α-β)推导过程

=1/2*ab*√(1-cos^2 c)
sin(a b) sin(b-a)/cos(a b)-cos(b-a)=-cota 证明
化简cos(a-b)cos(a-y)-sin(a-b)sin(y-a)
求不定积分∫dt/(a-b*cos(b-w*t))
sina sinb=1/2,cosa cosb=1/3,则cos(a-b)=