cos^2a-cos^2b=(cosa-cosb)(cosa+cosb)=-2cos[(a+b)/2]cos[(a-b)/2] *2sin[(a+b)/2]sin[(a-b)/2]=-sin(a+b)×sin(a-b)=1sin(a+b)×sin(a-b)=-1也可以反过来求sin(a+b)×sin(a-b)=-1/2(cos2a-cos2b)=-1/2[(2cos^2a-1)...