Question

1+2+3...+20=?




repede dau coroana​

Answer 1

Răspuns:

210

Explicație pas cu pas:

1+2+3...+20 = (1+20)·20:2 = 21·10 = 210

Answer 2

$\frac{n\cdot(n+1)}{2} = \frac{20\cdot21}{2} = \frac{420}{2} = 210$