2(sin a)^2+(2sin a*cos a)/(1+tan a)=k试用k表示sin a-cos aa∈(π/4，π/2）

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 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^2 A=sin^2 B+sinBsinC+sin^2 C 求A角 在三角形ABC中sin^A+sin^B=2sin^C,则角C为? 若sin^2a sin^2(-a)化简 sin(arccos(2sin(a)))= sin^2A+sin^2B=sin^2C求证△ABC的形状 求证数学题,在三角形ABC中,求证sin^2(A)+sin^2(B)+sin^2(C) 三角形ABC 证明sin(A/2)*sin(B/2)*sin(C/2) 证明 SIN²A+SIN²B-SIN²C=2SINASINBCOSC Sin ²A+sin²B+sin²C＜2,求三角形形状 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 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 a+sin 2a +sin 3a +...+sin na怎么求和? sin a+sin 2a +sin 3a +...+sin na怎么求和?