Question

6.Find the focus of the parabola using the general form of a parabola y = a(x – h)2 + k. The focus of a parabola is represented by the ordered pair (h, k + c). To find the value of c, recall that a = . Substitute the ordered pair of either corner of the box for x and y in the parabolic equation. The midpoint of (h, k) will be substituted for the variables h and k in the equation. Then, solve for c.

How do I find the, "a" variable?