Răspuns:
[tex] \frac{1}{a1} + \frac{1}{a2} - \frac{1}{a2} + \frac{1}{a3} - \frac{1}{a3} + .... \frac{1}{an - 1} - \frac{1}{an} = \frac{n - 1}{a1an} [/tex]
[tex] \frac{1}{a1} - \frac{1}{an} = \frac{n - 1}{a1an} \\ \frac{a1 - an}{a1an} = > an = a1 + n - 1 \\ = \frac{n - 1}{a1a \: n} [/tex]
pot
