2(b+c)=(a^2-a);
2(c-b)=a+3
4c=a^2+3
4b=a^2-2a-3=(a-3)(a+1)>0
a>3
4c-4a=a^2-4a+3=(a-3)(a-1)>0
最大角是边c对应的角;
cosC=(a^2+b^2-c^2)/2ab
=(a^2-1/4(a^2-a)(a+3))/2ab
=(4a-(a-1)(a+3))/2/(a-3)(a+1)
=1/2*(-a^2+2a-3)/(a^2-2a-3)
=-1/2
C=120°
2(b+c)=(a^2-a);
2(c-b)=a+3
4c=a^2+3
4b=a^2-2a-3=(a-3)(a+1)>0
a>3
4c-4a=a^2-4a+3=(a-3)(a-1)>0
最大角是边c对应的角;
cosC=(a^2+b^2-c^2)/2ab
=(a^2-1/4(a^2-a)(a+3))/2ab
=(4a-(a-1)(a+3))/2/(a-3)(a+1)
=1/2*(-a^2+2a-3)/(a^2-2a-3)
=-1/2
C=120°