解sin(A+B)-sin(A-B)=sinAcosB+cosAsinB-(sinAcosB-cosAsinB)=2cosAsinB即sin(A+B)+sin(A-B)=sinAcosB+cosAsinB+(sinAcosB-cosAsinB)=2sinAcosB即a^2[sin(A+B)-sin(A-B)]=b^2[sin(A+B)+sin(A-B)] 得 a^2sosAsinB=b^2sinAcosB