4x^n-2x^n-1-3x^n+2=x^(n-1)[4x-2-3x^2] 同时提取x^(n-1)
(4x^n-2x^n-1-3x^n+2)÷（-5x^n-1)=x^(n-1)[3x^2-4x+2]/x^(n-1)[5x]=
=(3x^2-4x+2)/(5x)