College Algebra, Chapter 8, Review Exercises, Section Review Exercises, Problem 2

Determine the vertex, focus and directrix of the parabola $\displaystyle x = \frac{1}{12} y^2$ and sketch the graph.

If we rewrite the parabola, we get $y^2 = 12x$. Now, the parabola has the form $y^2 = 4px$ with vertex at $(0,0)$ and opens to the right. The focus is determined to be $(p, 0)$ and the directrix $x = -p$. So if $4p = 12$, then $p = 3$. Thus, the focus lies on $(3,0)$ and the directrix is the line $x = -3$