(2mx^2-x^2+3x+1)-(5x^2-4y^2+3x)
=（2m-6)x^2+4y^2+1
与x无关即2m-6=0即m=3
于是
2m^2-[3m^2+(4m-5)+m]
=-m^2-5m+5
=-9-15+5
=-19