x的平方+2X-6=0
x^2=6-2x
x^3+5x^2+1
=x*(6-2x)+5x^2+1
=-2x^2+6x+5x^2+1
=3(6-2x)+6x+1
=18-6x+6x+1
=19
还有问题的话,欢迎追问