On the leg $B C$ of the right triangle $A B C$, a circle is constructed with $B C$ as its diameter, intersecting the hypotenuse $A B$ at point $P$. Chord $P Q$ is parallel to leg $B C$. Line $B Q$ intersects leg $A C$ at point $D$. It is known that $A C=b, D C=d$. Find $B C$.
Right triangles $A B C$ and $B D C$ are similar.

## Answer

$\sqrt{b d}$.