Question 595481
x2 + y2 - 2x+6y - 15 = X2 - 2X + Y2 + 6Y -15=0
                     = (X2 -2X +4)-4  + (Y2 +6Y +9)-9 = 0
                     = (X-2)^2 + (Y+3)^2 - 4 - 9 + 4 + 9= 4+9
                     = (X-2)^2 + (Y+3)^2 = 13

So the standard form is (X-2)^2 + (Y+3)^2 = 13