在△ABC中,sinA=5/13,cosB=3/5,求cosC的值cosC=-cos(A+B)=-cosAcosB+sinAsinB=-12/13×3/5+5/13×4/5=-16/65或cosC=-cos(A+B)=-cosAcosB+sinAsinB==12/13×3/5+5/13×4/5=56/65