b) va rog cat de repede puteti suma lui Gauss

1+2+3+...+2019=2019×(2019+1):2
=2019×2020:2
De aici sper ca stii :)))
2 x (1+2+3+...+2019) : 2020=
2 x (2019x2020)\2 : 2020=(simplific cu 2)
2019 x 2020 : 2020=
=2019 x 1
=2019
Succes!