Răspuns: 2019
Explicație pas cu pas:
[tex]\bf 2\cdot (1+2+3+...+2019): 2 020=[/tex]
[tex]\bf 2\cdot [(1+2019)\cdot 2019:2]: 2 020=[/tex]
[tex]\bf 2\cdot [2020\cdot 2019:2]: 2 020=[/tex]
[tex]\bf 2\cdot 2020\cdot 2019:2: 2 020=[/tex]
[tex]\boxed{~\bf 2019~}[/tex]
