Question: what is the vertex formula?
Answer: 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. in 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.