[tex]E=\frac{2}{3*(-1)^n}-\frac{1}{4*(-1)^{n+1}}+\frac{1}{2*(-1)^n} \\\\\\ \hbox{Se iau 2 cazuri, pentru n=2k-forma para si n=2k+1 -forma impara} \\\\\\ Caz \ 1 \to n-par \\\\\\ E= \frac{2}{3* 1}^{(4}-\frac{1}{4*(-1)}^{(3}+ \frac{1}{2*1} ^{(6} \\\\ E= \frac{8+3+6}{12} \\\\ \boxed{E=\frac{17}{12} } \\\\\\ Caz \ 2 \to n-impar \\\\ E=\frac{2}{-3}^{(4} -\frac{1}{4*1}^{(3}+ \frac{1}{-2} ^{(6} \\\\ E= \frac{-8-3+6}{12} \\\\ \boxed{E=-\frac{5}{12}}[/tex]
