[tex] \frac{2}{5} \leq \frac{2n+1}{3n+4} \leq \frac{4}{9} [/tex]
2(3n+4)=5(2n+1)=>6n+8=10n+5=> 4n=3=> [tex]n= \frac{3}{4} [/tex]
4(3n+4)=9(2n+1)=>12n+16=18n+9=> 6n=7=> [tex]n= \frac{7}{6} [/tex]
=> [tex] \frac{3}{4} \leq n \leq \frac{7}{6} [/tex]
sau 0,75 ≤ n ≤ 1,1(6)
De vreme ce n este natural => n=1
