Distances and sides

Write three tools for the distance formula and the sign test, and check them against a second method.

The idea. The distance of $(x_1, y_1)$ from $Ax + By + C = 0$ is $\dfrac{|Ax_1 + By_1 + C|}{\sqrt{A^2 + B^2}}$. Parallel lines $Ax + By + C_1 = 0$ and $Ax + By + C_2 = 0$ are $\dfrac{|C_1 - C_2|}{\sqrt{A^2 + B^2}}$ apart. Two points are on the same side when $Ax + By + C$ has the same sign at both.

Your tasks.

1. In distance, return the distance of the point (x1, y1) from the line.
2. In parallel_distance, return the distance between the two parallel lines with the same A and B.
3. In same_side, return True when the two points are strictly on the same side, and False otherwise. A point on the line is on neither side.