∵6mx^2+4nxy+2x+2xy-x^2+y+4
=(6m-1)x^2+(4n+2)xy+2x+y+4
其中不含二次项,
∴二次项系数6m-1=0,4n+2=0,
解得:m=1/6,n=-1/2
∴6m-2n+2
=6×1/6-2×(-1/2)+2
=1+1+2
=4