[tex]\it CA=CB \Rightarrow \Delta CAB\ -\ isoscel\\ \\ Fie\ F\in AB,\ FB=FA\ \ \ \ (1)\\ \\ CF\ e\ median\breve a\ \d si\ \hat\imath n\breve al\c{\it t}ime \Rightarrow CF\perp AB \ \ \ \ (2)\\ \\ \\ DA=DB \Rightarrow \Delta DAB\ -\ isoscel\\ \\ DF\ e\ median\breve a\ \d si\ \hat\imath n\breve al\c{\it t}ime \Rightarrow DF\perp AB \ \ \ (3)[/tex]
[tex]\it (2),\ (3) \Rightarrow C,\ F,\ D\ sunt\ coliniare,\ CD\perp AB \Rightarrow AB\perp CD\ \ \ \ (4)\\ \\ \\ (1),\ (4) \Rightarrow A\ e\ simetricul\ lui\ B\ fa\c{\it t}\breve a\ de\ dreapta\ CD\ .[/tex]
