sinA=1/2,sinB=1/3,sin(A+B)sin(A-B)=?
问题描述：
sinA=1/2,sinB=1/3,sin(A+B)sin(A-B)=?
答
=(sinacosb+sinbcosa)(sinacosb-sinbcosa)
=sina^2cosb^2-sinb^2cosa^2
=(1/2)^2[1-(1/3)^2]-(1/3)^2[1-(1/2)^2]
=2/9-1/12
=5/36