Reading a parabola

You will write functions that read the focus, the directrix and the latus rectum from $y^2 = Kx$, find the focal distance of a point and test whether a point is on the parabola. The checker uses the parabolas of the lesson.

The idea. For $y^2 = Kx$ we have $4a = K$. The focus is $(a, 0)$, the directrix is $x = -a$, the latus rectum is $4a = K$ and the focal distance of a point with abscissa $x_1$ is $x_1 + a$.

Your tasks.

1. Finish parts(K) to return (a, focus_x, directrix_x, latus_rectum).
2. Finish focal_distance(K, x1) to return the focal distance of the point of the parabola with abscissa x1.
3. Finish on_parabola(K, x, y) to return True if the point is on the parabola. Compare with a small tolerance.