Question 70
be $\omega$ and $\Omega$ two concentric circles (i.e. they have the same center) so that the circle $\omega$ either inside the circle $\Omega$. be $X$ and $Y$ Two points on the circle $\omega$. we note $P$ and $Q$ the respective intersection points of the circle $\Omega$ with the tangents in $X$ and $Y$ à $\omega$, so that $P$ and $Q$ are on the same side in relation to the line $(XY)$. Show that the points $X, Y, P$ and $Q$ are cocyclic.