a^2+a-1=0,
a^2+a+1=2
两边同乘以(a-1)
(a-1)(a^2+a+1)=2(a-1)
a^3-1=2a-2
a^3-2a=-1
3a^3-6a+3
=3(a^3-2a)+3
=3×(-1)+3
=0谢哦择了a