Rene Descartes was often sick so he was often on bed rest. He discovered the Cartesian Plane because of a fly that he saw on his tiled ceilings. Then, he wondered, what is the exact location of that fly.
x1, x2 = coordinates of the first point
y1, y2 =coordinates of the second point
d = square root (x2 - x1)^2 + (y2-y1)^2
