化简 2sin[a+b]cosa-sin[2a+b]如题

化简sin（a+B）cosa-1/2[ sin（2a+B）-sinB].过程谢谢 化简 2sin[a+b]cosa-sin[2a+b]如题 化简sin(a-b)*cosa - cos(a-b)*sina 为什么cosa-cosb=-2sin[(a-b)/2]*sin[(a+b)/2], 若sin(A+B)sin(B-A)=m,则(cosA)^2-(cosB)^2=? 已知sinA=1/5,求2sin(A+B)cosA-sin(2A+B) 求证：sin(a+b)cosa-(1/2)[sin(2a+b)-sinb]=sinb 求证cosa*sinb=1/2[sin(a+b)-sin(a-b)] 化简（sin(a+30)+sin(30-a)）/cosa得 三角形ABC中证明 COSA+COSB+COSC=1+4SIN(A/2)*SIN(B/2)*SIN(C/2) 三角形ABC中证明 COSA+COSB+COSC=1+4SIN(A/2)*SIN(B/2)*SIN(C/2) 化简:（sina+cosa)2一2sin a cos a Sin^4a+Sina*Cosa+Cos^2a化简 化简sin(a+30)+cos(a+60)/2cosa Rt三角形中 角c等于九十度 求证 sin^2A?tanA+sin^2B?tanB=1-2sin^2A?sin^2B/cosA?cosB 证明cosA＋cosB＋cosC=1+4sin(A/2)sin(B/2)sin(C/2)证明：cosA＋cosB＋cosC=1+4sin(A/2)sin(B/2)sin(C/2)尽量详细一点选做cosA+cosB+cosC=1+4sin(A/2)sin(B/2)sin(C/2) cos(180-B-C)+cosB+cosC=1+2sin(A/2)[2sin(B/2)sin(C/2)] cos(180-B-C)+cosB+cosC 化简1-2sin^2二分之a=cosa 求证：cosa(cosa-cosb)+sina(sina-sinb)=2sin^2a-b/2