create the equation of a circle that has center at (1,3) and a radius of 4 units

The equation of a circle with center at (h,k) and radius r is given by:

(x - h)^2 + (y - k)^2 = r^2

Substitute the given center (1,3) and radius 4 into the equation:
(x - 1)^2 + (y - 3)^2 = 4^2
(x - 1)^2 + (y - 3)^2 = 16

Therefore, the equation of the circle with center at (1,3) and radius of 4 units is:
(x - 1)^2 + (y - 3)^2 = 16