若n的平方+n-1=0
n^2+n=1
n^2=1-n
则n的立方+2n的平方+2011
=n^2(n+2)+2011
=(1-n)(n+2)+2011
=n+2-n^2-2n+2011
=2-n^2-n+2011
=2-(n^2+n)+2011
=2-1+2011
=2012