Question

(fracție)
1+2+3+...+n
----------------
21​

Answer 1

Coronița?

Folosim suma lui Gauss:)

=> [n*(n+1)/2] / 21

[n*(n+1)]/2 * 1/21

(n^2+n) / 42

Answer 2

[n(n+1)/2]/21 = [n(n+1)/2]* 1/21 = (n^2 +n)/42