Appendix A - Review - A.4 Factoring Polynomials - A.4 Assess Your Understanding - Page A40: 82

$(x-2)(x-4)$

To factor the second-degree polynomial $x^2 - 6x + 8$, we have to find integers whose product is $8$ and whose sum is $-6$. That is, we have $-2$ and $-4$ where $-2-4=-6$ and $-2\times (-4)=8$. Thus $$ x^2 - 6x + 8=(x-2)(x-4) .$$