Question

calculați: Sn=1+2+3+..+n​

Answer 1

Răspuns:

S = 1 + 2 + .. + n

S = n + .. + 2 + 1

2S = (n + 1) + (n - 1 + 2 ) + .. (n - 1 + 2) + (n + 1) de n ori

2S = (n + 1) + (n + 1) + .. + (n + 1) de n ori

2S = n(n + 1)

S = n(n + 1)/2