(2mx²-x²+3x+1)-(5x²+4y²+3x)
=2mx²-x²+3x+1-5x²-4y²-3x
=(2m-1-5)x²-4y²+1
则x²系数为0
2m-1-5=0
m=3
所以原式=2m²-3m²-4m+5-m
=-m²-5m+5
=-9-15+5
=-19
(2mx²-x²+3x+1)-(5x²+4y²+3x)
=2mx²-x²+3x+1-5x²-4y²-3x
=(2m-1-5)x²-4y²+1
则x²系数为0
2m-1-5=0
m=3
所以原式=2m²-3m²-4m+5-m
=-m²-5m+5
=-9-15+5
=-19