For any circle with Cartesian equation

,
we have that the centre of the circle is

, and the radius of the circle is

.
So in the case that

,
we essentially have that

.
So the centre of the circle is

, and the radius is

.
Answer:
They represent the rise and run of the graph.
Step-by-step explanation:
The difference between the x-axis of the points represents the "run" of the graph (or how much you should run along x-axis to get to the next point.)
The difference between the y-axis of of the points represents the "rise" of the graph (or how much you should rise up the y-xis to get to the next point).
The ratio of rise to run is the slope of the graph, which tells us how many steps should we take on the y-axis for every step we move forward on the x-axis.
To solve this problem you need to know the law of cosines.