Question 6
Let $\Gamma_{1}$ and $\Gamma_{2}$ be two circles meeting at two distinct points $A$ and $B$. Let $O$ be the centre of $\Gamma_{1}$. Let $C$ be a point of $\Gamma_{1}$, and let $D, E$ be the respective intersections of $(AC)$ and of $(BC)$ with $\Gamma_{2}$.
Prove that $(OC)$ and $(DE)$ are perpendicular.
Prove that $(OC)$ and $(DE)$ are perpendicular.