Find quadratic function from given vertex and a point

The vertex coordinates they provide are (-2, 5), and the point that the parabola passes through is (0, 9). First, I mentally imagined the points on a plane to determine whether "a" was positive or negative; then I took the coordinates from the vertex point, which represent (h, k), and sent up my problem. It came out to be y = (x + 1)^2 - 5, but in the answer key the 5 (which is k) was positive. Why is this so?

Re: Find quadratic function from given vertex and a point

You know in general a quadratic function looks like:

$\displaystyle y=a(x-h)^2+k$ with the vertex $\displaystyle (h,k)$ so in this case you know for sure the equation has to be:

$\displaystyle y=a(x+2)^2+5$

You only have to determine $\displaystyle a$ which can be done by enter the given point where the parabola goes through.