1.2asinA=(2b+c)sinB+(2c+b)sinC 正弦定理
2a^2=2b^2+bc+2c^2+bc
a^2=b^2+c^2+bc
cosA=(b^2+c^2-a^2)/2bc=-1/2 A=120°
2.A=120° B=60°-C
sinB+sinC=sin(6°-C)+sinC
=√3/2cosC-1/2sinC+sinC
=√3/2cosC+1/2sinC
=sin(C+60°)=1
C=30°
B=30°
△ABC的为等腰三角形