Question

calculați :
1+2+3+...+1999

Answer 1

1+2+3+...+1999=1999*(1999+1):2
=1999*2000:1
=3998000:2
=1999000
Formula: n*(n+1):2

Answer 2

E o suma Gauss, deci rezultatul este

$S_{1999}= \frac{1999\cdot2000}{2}=1999\cdot1000=1999000$