Test 3 Section 3 Number 12?

This is one of my favorite questions! All you’re told is that has its vertex at , and then you’re asked for an expression for *d*, the *y*-coordinate of the vertex.

The way to get this is to recognize that the factored form you’re given is already giving you the *x*-coordinate of the vertex. If the parabola can be factored to , then you know it has zeros at *x* = 2 and *x* = –4. Because all parabolas are symmetrical, you know that the *x*-coordinate of the vertex must be right smack between those zeros (i.e., at the average of those zeros). , so the *x*-coordinate of the vertex is –1.

Now all you need to do is plug –1 in for* x* to find the *y*-coordinate of the vertex.