sin(a-b)=5/13,sin(a+b)= -5/13且a-b∈（π/2,π）,a+b∈（3π/2,2π）,求cos2b的值

sin(a+b)cosa-cos(a+b)sina=5/13 则sin（π-B)=? 证明sin(a+b)sin(a-b)=sin^2 a-sin^2 b, 如何证明sin(a+b)sin(a-b)=sin*a-sin*b (*为平方) 求证恒等式sin(A+B)sin(A-B)=sin²A-sin²B 求证:sin(a+b)sin(a-b)=sin^2a-sin^2b 【证明】Sin A+sin B=2Sin 22 sin a-sin b等于 已知3SIN^2A+2SIN^2B=5SINA,求SIN^2A+SIN^2B范围 已知sin(a)=2sin(b)求sin(a/2)/sin(b/2)的值. 3 在三角形ABC中,已知（a2+b2）sin（A-B）=（a2-b2）sin(A+B) 求证：ABC是等腰或直角三角形(a^2+b^2)sin(A-B)=(a^2-b^2)sin(A+B),(sin^A+sin^B)sin(A-B)=(sin^A-sin^B)sin(A+B) sin^A*(sin(A+B)-sin(A-B))=sin^B*(sin(A-B)+sin(A+B)) sin^A*2c 角ABC sin A :sin B :sin C = 5 :6:8三角形最大余弦值 sin(a+b)sin(a-b)=sin2a-sin2b求证 求证：sin(A+B)sin(A-B)=sinAsinA-sinBsinB sin（a-b）=sin（a+b）吗? SIN(B-A)=-SIN(A-B)为啥 A,B为锐角,sin A=4/5,COS(A+B)=5/13,求sin B 求 sin(a+b)=? sin（a-b）=?