In this video,i've used a Wikipedia article which is available at https://fr.wikipedia.org/w/index.php?title=Tableau_de_signes&oldid=155167905 . There are more videos on this subject,also another playlists on different mathematical subjects on my youtube channel at; https://www.youtube.com/channel/UC_CwgOG-Yep1e8F9g9fH3vA/playlists
