sin^2 A=sin^2 B+sinBsinC+sin^2 C 求A角

求证：sin(a+b)cosa-(1/2)[sin(2a+b)-sinb]=sinb 证明sina sin(a+2b) - sinb sin(b+2a) =sin(a+b)sin(a-b) 急 sin^A=sin^B=sinC(sinB+sinC)三角形ABC中,若sin^A=sin^B=sinC(sinB+sinC),则角A=呃……是sin^2A=sin^2B+sinC(sinB+sinC) sinA=1/2,sinB=1/3,sin(A+B)sin(A-B)=? 求证cosa*sinb=1/2[sin(a+b)-sin(a-b)] 证明:sin(2a+b)/sinb-2cos(a+b)=sinb/sina急 sinb/sina=cos(a+b),证明3sinb=sin(2a+b) (sinA+sinB)(sinA-sinB) = 1/2 sinC^2是怎么化简成为sin(A+B)sin(A-B) = 1/2sin(A+B)^2 若arcsin(sinA + sin B) + arcsin(sinA - sinB) = π /2,求 (sin²A + sin²B) 的值. 三角形ABC中,已知（sin^2 A-sin^2 B-sin^2 C)/(sinB sinC)=1 求A? 在△ABC中,求证sin(A+B)/(sinA+sinB)+sin(B+C)/(sinB+sinC)+sin(C+A)/(sinC+sinA)>=3/2 sin(2a-b)-2cos(a+b)sina/sinb 在三角形ABC中.已知sin^2A+sin^2B*sin^2C=sinB*sinC+sinC*sinA+sinA*sinB,求证三角形ABC是等边三角形 证cosA+cos(120+B)+cos(120-B)/(sinB+sin(120+A)-sin(120-A)=tan(A+B)/2 为什么sinA-sinB/sinA+sinB=cos[(A+B)/2]sin[(A-B)/2]/{sin[(A+B)/2]cos[(A-B)/2]? 已知A、B为锐角,且sinA*sinA+sinB*sinB=sin(A+B),求证A+B=∏/2 已知cos(a+B)+1=0,求证sin(2a+B)+sinB=0?(提示:sin(-a)=-sina). 在三角形ABC中,若(a^2+b^2)sin(A-B)=(a^2-b^2)sin(A+B),则三角形是?a/sinA=b/sinB=k则a=ksinA,b=ksinB代入(a^2+b^2)sin(A-B)=(a^2-b^2)sinC并把k约分(sin²A+sin²B)sin(A-B)=(sin²A-sin²B)sin(A+B) sin²A*[sin(A+B)-sin(A-B)