a) [tex]4n^2+4n\ \textless \ (2n+1)^2 \ \textless \ =\ \textgreater \ 4n^2+4n\ \textless \ 4n^2+4n+1 (adevarat)[/tex] (1)
[tex](2n)^2 \leq 4n^2+4n \ \textless \ =\ \textgreater \ 4n^2 \leq 4n^2+4n (adevarat)[/tex](2)
din (1) si (2) => [tex](2n)^2 \leq 4n^2+4n\ \textless \ (2n+1)^2 \ \textless \ =\ \textgreater \ 2n \leq \sqrt{4n^2+4n} \ \textless \ 2n+[/tex]