Find the equation of the director circle of the ellipse x2a2+y2b2=1\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1a2x2+b2y2=1.
x2+y2=a2+b2x^2 + y^2 = a^2 + b^2x2+y2=a2+b2
x2+y2=a2−b2x^2 + y^2 = a^2 - b^2x2+y2=a2−b2
x2+y2=a2x^2 + y^2 = a^2x2+y2=a2
x2+y2=b2x^2 + y^2 = b^2x2+y2=b2