x2+5x-4=0
所以
x2+5x=4
x3+6x2+x+2
=x(x2+5x)+x2+x+2
=4x+x2+x+2
=x2+5x+2
=4+2
=6
x3+2x2+3
=x(x2+x)+x2+3
=x+x^2+3
=1+3
=4