Question

Calculați 3+6+9+12...2019

Answer 1

S=3+6+9+..+2019
S=3(1+2+3+..+673)  Aplicăm suma lui Gauss
S=3 × 
S= 3 ×
S=3×226801
S=680403
Baftă!

Answer 2

Nr term =2019-3 +1= 2016 +1 = 673 ---------- ------- 3 S= 673 ( 2019+3)=673·2022=673·1011 ------------------ ----------- 2. 2.