an = \frac{-2}{n+1}
źródło:
a_{n+1}-a_n=\frac{-2}{(n+1)+1}-\frac{-2}{n+1}=\frac{-2}{n+2}+\frac{2}{n+1}=\frac{-2n-2+2n+4}{(n+2)(n+1)}=\frac{2}{(n+2)(n+1)}>0 bo n>0 Ciąg rosnący