题目应是：若多项式（2mx²-x²+5x+8）-（5x²-3y+5x)的值与x的取值无关,求m³-（2m²-（5m-4）+m）的值（2mx^2-x^2+5x+8)-(5x^2-3y+5x)
=2mx^2-x^2+5x+8-5x^2+3y-5x
=2mx^2-6x^2+8+3y
=2(m-3)x^2+3y+8 多项式的值与x的取值无关,所以 m-3=0,m=3
m^3-[2m^2-（5m-4)+m]
=m^3-(2m^2-5m+4+m)
=m^3-2m^2+5m-4-m
=m^3-2m^2+4m-4
=3^3-2x3^2+4x3-4
=17