Question

2/9+3/48+...+1003/3012=?
3/9+4/12+...+1004/3012=?
4/9+5/12+...+1003/3018=?

Answer 1

Doar a doua suma e valida.
Celelalte sunt scrise greșit.

$\dfrac{3}{9}+\dfrac{4}{12}+...+\dfrac{1004}{3012} = \\ \\ = \sum\limits_{k=3}^{1004} \dfrac{k}{3k} = \sum\limits_{k=3}^{1004} \dfrac{1}{3} = \\ = \sum\limits_{k=1}^{1002} \dfrac{1}{3} = \dfrac{1}{3}\cdot 1002 = \\ \\ = \dfrac{1002}{3}=334$