Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$-(x+3)(x-5)$
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 $$-(x^2 -2x -15)=-(x+3)(x-5) .$$