# Unsolved ChallengeProve ∠PAB = ∠CAQ

#### anemone

##### MHB POTW Director
Staff member
The insphere and the exsphere opposite to the vertex $D$ of a (not necessarily regular) tetrahedron $ABCD$ touch the face $ABC$ in the points $P$ and $Q$, respectively. Show that $\angle PAB=\angle CAQ$.