The equation of a circle is
(x-h)² + (y-k)² = r²
for center (h, k) and radius r. Of course, the radius can be computed by putting the point in the equation.
(x-2)² + (y-3)² = (-1-2)² + (1-3)² = 9+4 = 13
The standard equation of the circle is (x-2)² + (y-3)² = 13.
