sin（a-b）=3/5,sin（a+b）=-3/5,a-b属于（π／2,π）a＋b属于（3π／2,2π）,则cos2b=?

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 sin（a-b）=sin（a+b）吗? 已知3SIN^2A+2SIN^2B=5SINA,求SIN^2A+SIN^2B范围 sin（a-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 sin a-sin b等于 锐角ABC.SIN（A+B）=3/5.SIN（A-B）=1/5求TAN（B） 【证明】Sin A+sin B=2Sin 22 sin(A+B)=4/5,sin(A-B)=-3/5,则tanA/tanB= sin(a+b)=1/3,sin(a-b)=1/5,则tana*cotb=? cos(a+b)cos(a-b)+sin(a+b)sin(a-b)=-3/5,求sin(3π/2+2b) 已知sin(a)=2sin(b)求sin(a/2)/sin(b/2)的值. 在△ABC中,求证；sin^(A/2)+sin^(B/2)+sin^(C/2)=1-2sin(A/2)sin(B/2)sin(C/2） sin(a+b)=-3/5,sin(b-π/4）=12/13,求cos（a+π/4)值 已知5sinB=sin（2A+B),求证2sin（A+B）=3tanA