Szczegółowe wyjaśnienie:
[tex]a_{n} =(-1)^{n} *\frac{1-n}{n}[/tex]
[tex]a_{2} =(-1)^{2} *\frac{1-2}{2} =1*(-\frac{1}{2})=-\frac{1}{2}[/tex]
[tex]a_{5} =(-1)^{5} *\frac{1-5}{5} =(-1)*(-\frac{4}{5} )=\frac{4}{5}[/tex]
[tex]a_{8} =(-1)^{8} *\frac{1-8}{8} =1*(-\frac{7}{8} )=-\frac{7}{8}[/tex]
[tex]a_{2} +a_{5} +a_{8} =-\frac{1}{2} +\frac{4}{5} -\frac{7}{8} =-\frac{20}{40} +\frac{32}{40} -\frac{35}{40} =-\frac{23}{40}[/tex]
