(2mx^2-x^2+3x+1)-(5x^2-4+3x)
=(2m-6)x²+5
∵不含有x²项
∴2m-6=0
∴m=3
2m^3-[3m^3-(4m-5)+m]
=2m³-3m³+4m-5-m
=-m³+3m-5
=-27+9-5
=-23