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2019x2x(1+2+3+...+2019) va rog nu e nevoie de explicați ​

Răspuns :

2019×2(1 + 2 + .. + 2019) =

= 2019×2×2019×2020 : 2

= 2019×2019×2020

= 2019²×2020

daca era + ...

2019 + 2(1 + 2 + .. + 2019) =

= 2019 + 2×2019×2020 : 2

= 2019 + 2019×2020

= 2019(1 + 2020)

= 2019×2020