Chapter 5 Polynomials and Polynomial Functions - 5.9 Write Polynomial Functions and Models - 5.9 Exercises - Skill Practice - Page 397: 9

$f(x)=\dfrac{2}{5}x(x+5)(x-6)$

We need to plug in $x=1$ and $y=-12$ in order to get the correct answer. Here, we have $y=a(x+5)(x)(x-6)$ $-12=a(1+5)(1)(1-6)$ or, $-12a=30a$ This gives: $a=\dfrac{2}{5}$ Thus, we have $f(x)=\dfrac{2}{5}x(x+5)(x-6)$