sin(A+B)=2sin(B+C)怎么推出sinC=2sinA?

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)=2sin(B+C)怎么推出sinC=2sinA? sin（A+B）=2sin（B+C）怎么化简成sinC=2sinA 求证(a^2+b^2-c^2)/(b^2+c^2-a^2)=(sin(A+B)+sin(A-B))/(sin(A+B)-sin(A-B)) 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+C)/2] =sin(π/2-B/2) 怎么算的 在三角形ABC中sin^A+sin^B=2sin^C,则角C为? a+b+c/sin A+sin B+sin C怎么证啊 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 sin^2 A=sin^2 B+sinBsinC+sin^2 C 求A角 【证明】Sin A+sin B=2Sin 22 sin^2A+sin^2B=sin^2C求证△ABC的形状 证明 SIN²A+SIN²B-SIN²C=2SINASINBCOSC 用正弦定理证明a+b/c=sin A+sin B/sin c 已知sin(a)=2sin(b)求sin(a/2)/sin(b/2)的值. a*sin(a)+b*cos(a)=sqrt(a^2+b^2)sin(a+c) [其中,tan(c)=b/a] 是怎么推导出来的? 三角函数公式的问题sin^A+sin^B=sin(A+B)sin(A-B)是怎么解得,sin^2A—sin^2B 是A B的平方，对不起打错了 就是这个，平方，