[tex]11.a)D_1_2=1,2,3,4,6,12\\
=\ \textgreater \ 2x+1=1=\ \textgreater \ x=0\\
=\ \textgreater \ 2x+1=2=\ \textgreater \ x=0,5\\
=\ \textgreater \ 2x+1=3=\ \textgreater \ x=1\\
=\ \textgreater \ 2x+1=4=\ \textgreater \ x=1,5\\
=\ \textgreater \ 2x+1=6=\ \textgreater \ x=2,5\\
=\ \textgreater \ 2x+1=12=\ \textgreater \ x=5,5\\\\
cum~x~apartine~N=\ \textgreater \ x=0,1\\\\
x+1=3=\ \textgreater \ x=2(divizor~propriu~al~lui~6=3)\\
x=2
[/tex]