Femhörningens vinkelsumma: https://www.geogebra.org/m/pxue2m7h Pythagoras sats: https://www.geogebra.org/m/dBu3hnqx Randvinkel: https://www.geogebra.org/m/jmabzrty Vinklar vid parallella linjer: https://www.geogebra.org/m/ztgesgr6 Proof without words (engelsk bok): https://www.geogebra.org/m/jFFERBdd Quadrilaterals (engelsk bok): https://www.geogebra.org/m/GFwZ5qdf Surface area and volume (engelsk bok): https://www.geogebra.org/m/s7TznqSP