Square root of 2 is irrational

In this short video (in German) I show that the square root of 2 is not a rational number. The notes as a PDF file are also available.
Tools: Neolab Smartpen M1 combined with Papertube.
Notice that the Neolab Smartpen requires a special paper, which can be bought separately or printed from a PDF. In the latter case, the printer must be somewhat above the average quality to ensure acceptable quality of slides/video.