sin(a+b)×sin(a-b)=-1/2(cos2a-cos2b)=-1/2[(2cos^2a-1)-(2cos^2b-1)]=-(cos^2a-cos^2b)=-tsin(a+b)sin(a-b)怎么看出来=的有公式吗直接用和差化积公式:-1/2(cos2a-cos2b)1/2*(cos2B-cos2A)=1/2*{-2sin[(2B+2A)/2]sin[(2B-2A)/2]}=-sin(B+A)sin(B-A)=sin(A+B)sin(A-B).