根据cosC=2cos^2(C/2)-1sinAsinB=0.5*(cosC+1)sinAsinB=0.5cos(pi-A-B)+0.5sinAsinB=-0.5cos(A+B)+0.5sinAsinB=-0.5cosAcosB+0.5sinAsinB+0.5sinAsinB+cosAcosB=1cos(A-B)=1A=B答案是等腰三角形