分类：教育/科学-学习帮助
问题：在三角形ABC中,sinAcos^2(C/2)+sinCcos^? 
求证：sinA+sin=2sinB
回答：sinAcos^2(C/2)+ sinCcos^2(A/2)
=1/2sinAcosC +1/2sinA +1/2 sinCcosA+1/2sinC
=1/2sin(A+C)+1/2 (sinA+sinC)
=1/2sinB +1/2(sinA+sinC)

1/2sinB +1/2(sinA+sinC) = 3/2sinB 

 =====>1/2(sinA+sinC)=sinB 
sinA+sinC=2sinB