Răspuns:
Explicație pas cu pas:
2 + 4 + 6 + ...+ 4040
4040 = 2 + (n - 1)*2 = 2 + 2n - 2 = 2n
n = 4040 : 2 = 2020 termeni in suma
2 + 4 + 6 + ...+ 4040 = 2020*(2 + 4040)/2 = 2020*4042/2 = 2020*2021
a = 2020*2021 - 2020 = 2020*(2021 - 1) = 2020*2020 = 4080400
a=(2+ 4 + 6 + … + 4040)-2020
a=(1×2+2×2+2×3+2×4+...+2×2020)-2020
a=2(1+2+3+....+2020)-2020
a=2×2020×(2020+1):2-2020
a=2020×2021-2020
a=2020(2021-1)
a=2020×2020
a=2020²
