Explicație pas cu pas:
a) 3+6+9+12+....+2019=
=(2019+3)×[(2019-3):3+1]:2
=2021×(2016:3+1):2
=2021×(672+1):2
=2021×673:2
=1 358 112:2
=679 056
b)5+10+15+20+......+2020=
=(2020+5)×[(2020-5):5+1]:2
=2025×(2015:5+1):2
=2025×(403+1):2
=2025×404:2
=2025×202
=409 050
c)4+8+12+....+2020=
=(2020+4)×[(2020-4):4+1]:2
=2024×(2016:4+1):2
=2024×(504+1):2
=2024×505:2
=1 022 120:2
=511 060
d)7+14+21+....+2023=
=(2023+7)×[(2023-7):7+1]:2
=2030×(2016:7+1):2
=2030×(288+1):2
=2030×289:2
=584 640:2
=292 320
Sper că te-am ajutat! Spor!
