(2mx2-x2+3x+1)-(5x-4y+3x)
=2mx2-x2+3x+1-5x+4y-3x
=(2m-1)x2-5x+4y+1
不含x2项则2m-1=0
m=1/2
2m3-[3m3-(4m-5)+m]
=2m3-3m3+(4m-5)-m
=-m3+3m-5
=-1/8+3/2-5
=-29/8
(2mx2-x2+3x+1)-(5x-4y+3x)
=2mx2-x2+3x+1-5x+4y-3x
=(2m-1)x2-5x+4y+1
不含x2项则2m-1=0
m=1/2
2m3-[3m3-(4m-5)+m]
=2m3-3m3+(4m-5)-m
=-m3+3m-5
=-1/8+3/2-5
=-29/8