The equation of a circle is defined by (x – h)² + (y – k)² = r² with the center being at (h, k) and with radius r. So for this circle with center at (0, 0) and r = 13 the equation is x² + y² = 169. Then we plug in the ordered pairs: (-5, 12) (-5)² + (12)² = 169 25 + 144 = 169 is true.