已知 sin a +sin b =1/4cos a +cos b =1/3求 tan (a+b)

已知sin(a)=2sin(b)求sin(a/2)/sin(b/2)的值. 已知 sin a +sin b =1/4cos a +cos b =1/3求 tan (a+b) 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sina=2/3,cosb=-1/4,a b为相邻象限的角,求sin(a=b)与sin(a-b)的值求sin(a+b)与sin(a-b) 已知sin(a+b)=1/3,sin(a-b)=1/4,求tana/tanb的值. 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 已知A+b+C=π 求证 cosA+cosB+cosC=1+4sin(A/2)sin(B/2)sin(C/2) 三角形ABC中,已知（sin^2 A-sin^2 B-sin^2 C)/(sinB sinC)=1 求A? 已知sin^4a/cos^2b+cos^4a/sin^2b=1,求证:sin^4 b/cos^2 a+cos^4b/sin^2a=1 已知(cos^4a)/cos^2b+(sin^4a)/sin^2b=1求证(cos^4b)/cos^2a+(sin^4b)/sin^2a=1 已知sin acos b=1,则sin(a-b)= 已知sin(a+b)等于2/3,sin(a-b0 =1/5,求tana:tanb 已知3SIN^2A+2SIN^2B=5SINA,求SIN^2A+SIN^2B范围 已知sin[a-b]cos a-cos[b-a]sin a=3/5,b是第三象限角,求sin[b+5π/4]的值第一题1/2cos x-√3/2sin x第二题√3sin x+cos x第三题√2[sin x-cos x]第四题√2cos x-√6sin x 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)