Răspuns :
Facem de la dreapta la stânga.
[tex]\frac{1}{n}-\frac{1}{n+1}=\frac{n+1}{n(n+1)}-\frac{n}{n(n+1)}=\frac{n+1-n}{n(n+1)}=\frac{1}{n(n+1)}[/tex]
[tex]\frac{1}{n}-\frac{1}{n+1}=\frac{n+1}{n(n+1)}-\frac{n}{n(n+1)}=\frac{n+1-n}{n(n+1)}=\frac{1}{n(n+1)}[/tex]
[tex] \frac{1}{n(n+1)} = \frac{n-n+1}{n(n+1)}= \frac{n+1}{n(n+1)}- \frac{n}{n(n+1)} = \frac{1}{n} - \frac{1}{n+1} [/tex]