[tex] \left \{ {{} \atopx~x~apartine~N|2x+1\ \textgreater \ 18 {}} \right. \\
(x~apartine~N~cu~proprietate~ca:2x+1~maimare~decat~18)\\
=\ \textgreater \ 2x+1\ \textgreater \ 1`8=\ \textgreater \ 2x\ \textgreater \ 17+\ \textgreater \ x\ \textgreater \ 8,5\\
Cum~x~apartine~N=\ \textgreater \ x=9,10,11,12,13,...,infinit[/tex]
