(x+1)(2x+1)(3x-1)(4x-1)+6x^4=(3x^2+2x-1)(8x^2+2x-1)+6x^4=(3x^2+2x-1)(5x^2+3x^2+2x-1)+6x^4=(3x^2+2x-1)^2+5x^2(3x^2+2x-1)+6x^4=(3x^2+2x-1+2x^2)(3x^2+2x-1+2x^2)=(5x^2+2x-1)(6x^2+2x-1)