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21. Calculaţi:
a) (1 + 2 + 3 + ... +2 018): 2 019;
b) 2. (1 + 2 + 3 + ... +2 019): 2020.​


Răspuns :

Răspuns:

Aplicăm formula lui Gauss

(1+2+3+....+2018) = 2018×(2018+1)

= 2018×2019 | : 2019

= 2018

(1+2+3+4+.....+2019) = 2019×(2019+1)

=2019 × 2020 | : 2019

= 2020