1.1.2. Mulțimi de numere – clasa a X-a,
https://matematic.eu/Clasa9/Numere%20reale_formule.pdf
https://www.edumo.org/capitol/4952389618499584
https://www.edumo.org/capitol/5612009085206528
https://www.edumo.org/capitol/5651488961462272