(x^2+2x)^2-2
= (x^2+2x+根号2)(x^2+2x-根号2)
= (x^2+2x+根号2) { (x+1)^2-(根号2+1) }
= (x^2+2x+根号2) { (x+1+根号(根号2+1) } { (x+1 - 根号(根号2+1) }