The three triangles: Tangram from G. Brügner
<a href="//commons.wikimedia.org/wiki/User:Sarang" class="mw-redirect" title="User:Sarang">Sarang</a>
Own work based on: <span style="border:1px dotted #FC0;padding:0 4px"><a href="https://de.wikipedia.org/wiki/File:Drei-Dreiecke-Tangram_Winkel.svg" class="extiw" title="de:File:Drei-Dreiecke-Tangram Winkel.svg">Drei-Dreiecke-Tangram Winkel.svg</a></span> <i>by</i> <a href="//commons.wikimedia.org/wiki/User:McSush" title="User:McSush">McSush</a>