def equation(self) -> str:
    (x, y) = self.center
    return f'x^2 + 2*{(- x)}*x + 2*{(- y)}*y + y^2 + {(((x ** 2) + (y ** 2)) - (self.radius ** 2))} = 0'
def equation(self) -> str:
    (x, y) = self.center
    return f'x^2 + 2*{(- x)}*x + 2*{(- y)}*y + y^2 + {(((x ** 2) + (y ** 2)) - (self.radius ** 2))} = 0'