Chapter 10.5, Problem 5CV

To determine

To fill: The equation that is satisfied, which is obtained by rotation of the axes through an acute angle $\theta$ to transform $A{x}^2+Bxy+C{y}^2+Dx+Ey+F=0$ $B\ne 0$ into one in $x\text{'}$ and $y\text{'}$ without an $x\text{'}y\text{'}$-term.