:sin a * cos b + cos a * sin b / cos a * cos b - sina * sin

化简[sin(2A+B)]/sinA-2cos(A+B) cosb=cos[(a+b)-a]=cos(a+b)cosa+sin(a+b)sina 由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 用三角形证明 cos(a+b)+cos(a-b)/sin(a+b)+sin(a-b)化简 化简 cos(a+b)cosa+sin(a+b)sina=_______ cos(31°-a)cos(29°+a)-co 为什么sin(a+b)-sina=2sin（b/2）cos（a+b/2） 证明三角函数等式sin(A+B)-sinA=2cos(A+B/2)sin(B/2) 若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a 化简 sin^4a-cos^4b 求证:cos(a+b)cos(a-b)=cos平方b-sin平方a cos(a-b)cos(b-c)+sin(a-b)sin(b-c)=