Chapter 4 Quadratic Functions and Factoring - 4.10 Write Quadratic Functions and Models - 4.10 Exercises - Skill Practice - Page 312: 19

$y=\frac{1}{2}(x+3)(x-3)$

We already know $y$, $x$, $p$ and $q$ from the given x-intercepts and the point, so in order to get the quadratic function we need to find $a$... $y=a(x-p)(x-q)$ $-4=a(1+3)a(1-3)$ $-4=-8a$ $a=\frac{4}{8}$ $a=\frac{1}{2}$ Therefore the function is... $y=\frac{1}{2}(x+3)(x-3)$