(2mx^2-y^2+3x+1)-(5x^2-5y^2+3x)
=2mx^2-y^2+3x+1-5x^2+5y^2-3x
=(2m-5)x^2+4y^2+1
与x无关
所以x^2系数是0
2m-5=0
m=5/2
4m^2-(4m—5）+6m
=4m^2+2m+5
=4×25/4+2×5/2+5
=35