Question

已知x的二次方+x-1=0,求x的三次方+2x的二次方+3

Answer 1

x^2+x-1=0

x^2+x=1

x^3+2x^2+3

=x^3+x^2+x^2+3

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

=x+x^2+3

=1+3=4