Răspuns:
19+20+21+22+...+39=
39×(39+1):2=
39×40:2=
1.560:2=
=780
Aplicam formula pentru sume gauss :
[tex] \frac{n(n + 1}{2} [/tex]
[tex] \frac{39(39 + 1)}{2} [/tex]
[tex] \frac{39 \times 40}{2} [/tex]
=780.
