Appendix A - Review - A.4 Factoring Polynomials - A.4 Assess Your Understanding - Page A40: 87

$-(x+3)(x-5)$

For the polynomial $-(x^2 -2x -15)$ we have to find integers whose product is $-15$ and whose sum is $-2$. That is, we have $3$ and $-5$ where $3-5=-2$ and $3\times (-5)=-15$. Thus $$ -(x^2 -2x -15)=-(x+3)(x-5) .$$