There is a unique circle with a given center and radius

We can clearly see a circle with center ‘A’ and radius ‘r’. Coordinates of A are (x_1,y_1). We can change the values of x_1,y_1 and r using their respective slide bars and see how the size and position of the circle gets changed
Questions to think about How many circles do we get when we assign unique values to x_1,y_1 and r? Is it possible to get more than one circle with fixed values of x_1,y_1 and r?