4x^2n-3x^2＝x^2[4x^(2n-2)-3]-1/4x^n+1-1/2x^n+1/8x^n-1=-1/8x^n-1 乘 （ ）-1/4x^n+1-1/2x^n+1/8x^n-1=-1/8x^n-1 乘 （2x^2+4x-1 ）答一送一呀