Question

What is Director circle?

Answer

Director circle is that when a pair of tangents intersects to a central conic which are at right angles to each other. The equation of the director circle is $\left(\mathrm{ab}-h^2\right)\left(x^2+y^2\right)-2\left(\mathrm{hj}-\mathrm{bg}\right)x-2\left(\mathrm{gh}-\mathrm{af}\right)y+c\left(a+b\right)-\left(f^2+g^2\right)=0$