Formulate the equation of a circle that has a radius of 5 with its center at (1, -2).
The equation of the circle is (x-1)^2 + (y+2)^2 = 5^2, which is equivalent to the equation x^2 + y^2 = 25 - x^2 - y^2.
The equation of the circle is x^2 + y^2 = 10.