则n的3次方=2n的平方=2008的值是多少?
应该是n^3+2n^2+2008的值是多少吧?
n^2+n-1=0
n^2+n=1
n^3+n^2=n
n^3+2n^2=n^2+n
即n^3+2n^2=1
代入上式,得
n^3+2n^2+2008=1+2008=2009