[tex]E(x)=(\frac{x+1}{x}-\frac{x}{x+1}):(\frac{1}{x^2}-\frac{1}{(x+1)^2})\\
E(x)=\frac{(x+1)^2-x^2}{x(x+1)}:\frac{(x+1)^2-x^2}{x^2\cdot (x+1)^2}\\
E(x)=\frac{(x+1)^2-x^2}{x(x+1)}\cdot \frac{x^2\cdot (x+1)^2}{(x+1)^2-x^2}\\
E(x)=x(x+1)\forall x\in R - \{0,-1\}\\
Deci\ E(x)\ este\ numar\ par.[/tex]