已知sin(a+b)=1/2,sin(a-b)=1/3 求证：sina.cosb=5cosa.sinb （ 2）tana=5tanb拜托各位大神

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 已知sin(a+b)=1/2,sin（a-b)=1/3,求tana/tanb 已知sin(A+B)=2/3,sin(A-B)=1/5.求tanA/tanB 已知sinA=1/5,求2sin(A+B)cosA-sin(2A+B) 懂得进.证明,sina+sin(a+b)+sin(a+2b)+...sin(a+nb)=sin(a+ab/2)sin[(n+1)b/2]/sin(b/2) 已知3SIN^2A+2SIN^2B=5SINA,求SIN^2A+SIN^2B范围 三角形ABC中,已知（sin^2 A-sin^2 B-sin^2 C)/(sinB sinC)=1 求A? 已知sin(a+b)等于2/3,sin(a-b0 =1/5,求tana:tanb 已知 tan a =1 3sin(a+b)=sin(2a+b) ,求 tan(a+b) 的 值. 证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2B=1 证明sin(a+b)sin(a-b)=sin^2 a-sin^2 b, 求证:sin(a+b)sin(a-b)=sin^2a-sin^2b 已知 sin a,sin 2x ,cos a 成等差数列,sin a ,sin x ,cos a 成等比数列,求cos 2x 的值.已知 ,3sin^2 a+2sin^2 b=1 ,3sin 2a-2sin 2b=0 且a ,b 为锐角,试求 a+2b的值. 【证明】Sin A+sin B=2Sin 22 已知sin(A+B)=3/5,sin(A-B)=1/5,证明：tan A=2tan B. 已知sin(a+b)sin(a-b)=-1/3,求cos^2a-cos^2b的值 已知 3sin A = sin (2B +A ),求证 ： tan（A+B)= 2tanB