1.a-(2a+b)+(3a-4b)=_____________.2.多项式____与m²+m-2的和是m²-2m
3.4x2－[6x－(2x－3)＋2x2]＝_____________． 4.(8x²y-xy²）-4（x²y-4分之1xy²）_____________
7．化简n－mn－3(－m－n)－(－m)－11
填空
m2-2n2减去5m2-3n2+1的差为________.