Update cheatsheet.en.md

01.curriculum/01.physics-chemistry-biology/03.Niv3/02.Geometrical-optics/02.geometrical-optics-foundings/05.fermat-application/02.fermat-application-overview/cheatsheet.en.md

@@ -67,13 +67,17 @@ _Total reflection phenomenon_
 1) DIFFICULT : geogebra animation should spend over 100% of the window width, and keep its correct ratio width / height.
 2) VERY DIFFICULT: make sure that in connection mode, the animated image corresponding to the geogebra is displayed as long as the animation iframe geogebra is not downloaded, then it does not appear when the geogeba is ready, and that it is displayed in offline mode".-->
 
-<!--iframe width="auto" height="auto" sandbox="allow-same-origin allow-scripts" src="https://www.geogebra.org/material/iframe/id/bg5ewxee" frameborder="0" allowfullscreen></iframe-->
+<!--
+<!iframe width="auto" height="auto" sandbox="allow-same-origin allow-scripts" src="https://www.geogebra.org/material/iframe/id/bg5ewxee" frameborder="0" allowfullscreen></iframe>
 
 _smartphone : switch to "landscape" mode to see the geogebra animations._
 <iframe width="640" height="360" sandbox="allow-same-origin allow-scripts" src="https://www.geogebra.org/material/iframe/id/bg5ewxee" frameborder="0" allowfullscreen></iframe>
 <!--image gif correspondante-->
+
 ![](Opt_Geo_refle_lim_650.gif)
 
+animation : https://www.geogebra.org/material/iframe/id/bg5ewxee
+