sin(x+y)cos(x-y)+cos(x+y)sin(x-y)
=sin(x+y+x-y)
=sin2xsin(x+y)cos(x-y)+cos(x+y)sin(x-y)为什么=sin(x+y+x-y)公式是吗是 sin(a+b)=sinacosb+cosasinbtanA=tan[(A-B)+B]=[tan(a-B)+tanB]/[1-tan(A-B)*tanB]也是公式吗嗯 tan(a+b)=(tana+tanb)/(1-tanatanb)