$\left.\begin{array}{l}{[\text { Inscribed quadrilateral with perpendicular diagonals ] }} \\ {[\quad \text { Pythagorean Theorem (direct and inverse). }}\end{array}\right]$

A circle with radius 2 is circumscribed around a quadrilateral $ABCD$ with perpendicular diagonals $AC$ and $BD$. Find the side $CD$, if $AB=3$.
Draw the diameter $D D_{1}$.

## Answer

$\sqrt{7}$.