（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=0m=...