sin^2A+sin^2B=sin^2C=sin^2(A+B)=(sinAcosB+sinBcosA)^2=sin^2Acos^2B+sin^2Bcos^2A+2sinAcosAsinBcosB左边减右边sin^2A-sin^2Acos^B=sin^2A(1-cos^2B)=sin^2Asin^2Bsin^2B-sin^2Bcos^2A=sin^2B(1-cos^2A)=sin^2Asi...