已知sin(a+b)sin(a-b)=1/3,求证：1/4sin2a．sin2a+sinb.sinb+cosa.cosa.cosa.cosa为定值．我不会打平方和四次方,只好搞成相乘了~我做的求证的那堆东东等于cosa.cosa+sinb.sinb.前面的推出：(sinacosb+cosasinb)(sinacosb-

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) 已知sin(a+B)sin(a-B)=1/3,求cos2b-cos2a 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 tan a =1 3sin(a+b)=sin(2a+b) ,求 tan(a+b) 的 值. 已知3SIN^2A+2SIN^2B=5SINA,求SIN^2A+SIN^2B范围 已知sin acos b=1,则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 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 已知sin(a+b)等于2/3,sin(a-b0 =1/5,求tana:tanb 已知 sin a +sin b =1/4cos a +cos b =1/3求 tan (a+b)