在△ABC中,内角A,B,C的对边分别为a,b,c,已知sinB/(sinA+sinC)=1-si

sinB/(sinA+sinC)=1-sinC/(sinA＋sinB)，
b/(a+c)=1-[c/(a+b)]
整理得
b^2+c^2-a^2=bc
cosA=(b^2+c^2-a^2)/2bc=bc/2bc=1/2
cosA=1/2
A=π/3
2)acosC＝-1.
a^2[1-(sinC)^2]=1
(sinC)^2]=(a^2-1)&