Raymond J. answered 01/15/21
Patient with Ability to Explain in Many Ways
The equation of a parabola is (x-h)2 = 4p(y-k) for a parabola pointing up or down, (y-k)2 = 4p(x-h) for a parabola pointing left or right.
The vertex is (h, k) and p is the distance from the vertex to the directrix.
Since the directrix is y = 3, we know the parabola is pointing up or down. It opens up if 4p > 0, and it opens down if 4p < 0.
So we know h = 1, and k = 4.
If the directrix is y = 3, we need to find the distance from vertex to directrix, which is 4 - 3 = 1 = p
Since p = 1, 4p > 0 so this parabola opens up.
(p is also the distance from the vertex to the Focus, Focus = (h, k+p).
Now that we know p, h, and k, we can write the equation of the parabola:
(x-1)2 = 4(y-4)