Explicație pas cu pas:
a)
[tex] \frac{1}{11} < \frac{1}{2n + 1} < 1 \\ 11 > 2n + 1 > 1 \\ 10 > 2n > 0 \\ 5 > n > 0[/tex]
=> n ∈ {1; 2; 3; 4}
b)
[tex] \frac{28}{38} < \frac{14}{2n + 3} < 2 \\ \frac{2}{38} < \frac{1}{2n + 3} < \frac{2}{14} \\ \frac{1}{19} < \frac{1}{2n + 3} < \frac{1}{7} \\ 19 > 2n + 3 > 7 \\ 19 - 3 > 2n > 7 - 3 \\ 16 > 2n > 4 \\ 8 > n > 2 [/tex]
=> n ∈ {3; 4; 5; 6; 7}
