整理：6mX²+4nxy+2x+2xy-X²+y-4
=（6m-1）x^2+（4n+2）xy+2x+y-4
因为不含二次项,
所以6m-1=0,
4n+2=0,
所以m=1/6,n=-1/2
所以6m-2n+2=1+1+2=4