This is the question we looked at right at the end of the class. A couple of notes to the solution:
- I took a tiny shortcut in finding an expression for a, by working out an expression for c in terms of a. If you don’t like this method, you can easily substitute in the known point (0, -4) and solve for a that way.
- The fact that you were give then zeroes in the question should point you to using the factored form first. If you had been given the coordinates of the vertex, it would have been sensible to start with vertex form.