如果x2-2x-1=0,那么x3+x2-7x+4的值是 .

问题描述:

如果x2-2x-1=0,那么x3+x2-7x+4的值是 .

由x^2-2x-1=0,得,x^2-2x=1,代人,
x^3+x^2-7x+4
=x^3-2x^2+3x^2-7x+4
=x(x^2-2x)+3x^2-7x+4
=x+3x^2-7x+4
=3x^2-6x+4
=3(x^2-2x)+4
=3+4
=7