sin[(A+C)/2] =sin(π/2-B/2) 怎么算的

在△ABC中,求证；sin^(A/2)+sin^(B/2)+sin^(C/2)=1-2sin(A/2)sin(B/2)sin(C/2） 在三角形ABC中sin^A+sin^B=2sin^C,则角C为? 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^2 A=sin^2 B+sinBsinC+sin^2 C 求A角 sin^2A+sin^2B=sin^2C求证△ABC的形状 证明 SIN²A+SIN²B-SIN²C=2SINASINBCOSC sin[(A+C)/2] =sin(π/2-B/2) 怎么算的 已知A,B,C∈(0,π) 若有A+B+C=π,试证：sin(2/A)+sin(B/2)+sin(C/2)≤3/2 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)) 【证明】Sin A+sin B=2Sin 22 sin(arccos(2sin(a)))= 已知A+b+C=π 求证 cosA+cosB+cosC=1+4sin(A/2)sin(B/2)sin(C/2) sin(2π+a) ,sin(π+a),sin(5π+a) 的区别为什么sin(2π+a) =sina sin(π+a)=-sina 三角形abc中,2B=A+C,则sin^2A+sin^2C属于 在△ABC中,sin^2A+sinAsinB=sin^2C-sin^2B,则∠C= △ABC中sin^2A-sin^2C=根号2sinAsinB-sin^2B+则角C为 在△ABC中 若sin^2A+sin^2B=2sin^2C 则∠C为? 在三角形ABC中,sin^2A-sin^2C+sin^2B=sinAsinB,则角C为?