已知代数式（2mx²-x²+3x+1）-[-(-5x²+4 y²)+3 x]的值

（2mx²-x²+3x+1）-[-(-5x²+4 y²)+3 x]
=（2mx²-x²+3x+1）+ (-5x²+4 y²)-3 x
=2mx²-x²+3x+1-5x²+4 y²-3 x
=2(m-3)x²+1+4 y²]的值与x无关
m-3=0
m=3
3m²-[2m²-(4m+5)+m]
=3m²-2m²+(4m+5)-m
=3m²-2m²+4m+5-m
=m²+3m+5
=3^2+3*3+5
=23