1.(x^2+x-42)/(x+7)=(x+7)(x-6)/(x+7)=x-62.该是3x-3y[(x^2-2xy+y^2)+(3x-3y)+2]/(x-y+1)=[(x-y)^2+3(x-y)+2]/(x-y+1)=(x-y+1)(x-y+2)/(x-y+1)=x-y+2
