Chapter 10.4, Problem 4PE

The conic section defined by $A{x}^2+Bxy+C{y}^2+Dx+Ey+F=0$ will have no rotation relative to the new coordinate axes $x\text{'}$ and $y\text{'}$ if the $x\text{-}$ and $y\text{-axes}$ are rotated through an angle $\theta$ satisfying the relationship $\cot 2\theta =\text{\_\_\_\_\_\_}$ (answer in terms of $A,B,$ and $C$ ).