Relationship Between Pythagorean Theorem and Circle Equation

As we all know, the Pythagorean Theorem is a²+b²=c². The circle formula is

r²=(h-x)²+(y-k)². The hypotenuse can be drawn in a circle from the center, or (h,k), to any point on the circle, or(x,y), thus making c² the equivalent to r². The side a² can be taken from the point on the circle, which is on the y axis, and then to the y value of the center. So (y-k)² is the same as a². The side b² comes from the same place as the side a², but is on the x axis, so it goes from point x to point x in the center, or h.