求证：sin(a+b)cosa-(1/2)[sin(2a+b)-sinb]=sinb

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)] 求证：cosA°sinB°=1/2【sin（A+B）°-sin（A－B）°】 求证：cosa(cosa-cosb)+sina(sina-sinb)=2sin^2a-b/2 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 已知A+b+C=π 求证 cosA+cosB+cosC=1+4sin(A/2)sin(B/2)sin(C/2) 求证：(cosa-1)^2+sin^2a=2-2cosa 若cosA-2sin(A-B)=0,求证:tan(A-B)=cosB/(sinB+2) sin(A-B)=0,求证cos(A-2B)=cosA 若sina+cosb=1,cosa+sinb=根号2,求证sin(a+b)=1/2 已知Sin(a+b)=二分之一,Sin(a-b)=三分之一,(1)求证,Sina*cosb=5cosa*Sinb (2)tana=5tanb 求证：1/2(cos2B-cos2A)=sin(A+B)sin(A-B)(一定要从1/2(cos2B-cos2A）推到sin(A+B)sin(A-B)不可以像这样：/2（cos2B-cos2A)=1/2[2(cosB)^2-1-2(cosA)^2+1]=(cosB)^2-(cosA)^2sin(A+B)sin(A-B)=(sinAcosB+cosAsinB)(sinAcosB-cosAsinB)=(sinAcosB)^2-( ABC都是锐角,且cosA+cosB+cosC=1+4sin(A/2)sin(B/2)sin(C/2)设A.B.C都是锐角,且cosA+cosB+cosC=1+4sin(A/2)sin(B/2)sin(C/2)求证：A+B+C=180 求证sin(3π/2-a)=-cosa 求证sin(3π/2+a)=-cosa 求证：sin(3/2π+a)=-cosa 求证1+2sina cosa/sin^2a-cos^2a=tana+1/tana-1 求证：1+2sina cosa /sin^2a -cos^2a = tana +1/tana -1.