The vertex form of a quadratic is given by
y = a(x – h)2 + k, where (h, k) is the vertex.
The "
a" in the vertex form is the same "a" as
y = ax2 + bx + c (that is, both a's have exactly the same value). The sign on "a" tells you whether the quadratic opens up or opens down. Think of it this way: A positive "a" draws a smiley, and a negative "a" draws a frowny. (Yes, it's a silly picture to have in your head, but it makes is very easy to remember how the leading coefficient works.)