x^3+(2a+1)x^2+(a^2+2a-1)x+a^2-1 =x^2(x+1)+2ax(x+1)+a^2(x+1)-(x+1) =(x+1)*(x^2+2ax+a^2-1) =(x+1)〔(x+a)^2-a^2+a^2-1〕 =(x+a)(x+a-1)(x+a+1)
