cosA=5/13,cos(A+B)=-4/5,A.B都为锐角,则sinB=?
问题描述:
cosA=5/13,cos(A+B)=-4/5,A.B都为锐角,则sinB=?
答
∵A.B都为锐角
∴sinA=12/13,sin(A+B)=3/5
sinB=sin(A+B-A)
=sin(A+B).cosA-cos(A+B).sinA
=3/5×5/13-(﹣4/5)×12/13
=63/65