1.1.3. Șiruri – clasa a IX-a
https://matematic.eu/Clasa9/Progresii%20aritmetice.pdf
https://matematic.eu/Clasa9/Progresi%20aritmetice%20si%20geometrice.pdf
https://matematic.eu/Teorie_probleme/ProgresiiBac2010-2016.pdf
https://www.edumo.org/capitol/5828269278494720