∵mx²+2nxy-x+x²-2xy+y
＝(m+1)x²+(2n-2)xy-x+y
结果中不含2次项,则
m+1=0,2n-2=0
∴m=-1,n=1
∴3m-2n
=3×(-1)-2×1
=-3-2
=-5