# function from graph with no y intercept

Find the function from the following graph below:

I can see the graph has roots at -3 and 6 so normally I would plug the points into the form of:

$f(x) = k(x - a)(x - b)(x - c)$

But I am unsure what to do with no y intercept.

• I would absolutely love to know why this is voted down – dagda1 Mar 6 '16 at 10:16

You also have a root at $1$, so that gives you $a,b,c$. Then note the point $(3,-12)$. That tells you $f(3)=-12$ Plug that in to find $k$
Use the root at x=1 also. Differentiate (for minimum) to get second degree and plug in $x=3, y=-12$ to determine $k.$