So I was watching a video on Khan academy that explains how to find the equation of a parabola, given we have a focus and a directrix.
He draws a picture like this, the focus is at $(a, b)$ and we pick a random point on the parabola at $(x, y)$, the directrix is at $y = k$
The instructor indicates that we want to use the distance formula to help us with that.
What I don't understand, how can we apply the distance formula here? Where is the right triangle in that picture he drew?