Question

已知x的平方+x-1=0,求x的立方-2x+4

Answer 1

x^2+x-1=0

x^2-1=-x

两边同除以x

x-1/x=-1

x^3-2x+4

=x^3-x-x+4

=x^2(x-1/x)-x+4

=-x^2-x+4

=-(x^2+x-1)+3

=0+3

=3