Cho \(x = \frac{a}{{2{a^2} + 1}}\)

Với giá trị nào của a thì x là số hữu tỉ dương?

\(\dfrac{2}{13}\)

\(\dfrac{13}{-2}\)

\(\dfrac{-2}{13}\)

\(\dfrac{-13}{2}\)

\(-2\)

\(\dfrac{1}{2}\)

\(\dfrac{-1}{-2}\)

\(\dfrac{-1}{2}\)

\( - \frac{3}{5}\)

\(\frac{7}{{20}}\)

- \(\frac{7}{{20}}\)

\(\frac{{ - 35}}{{10}}\)

5

4

3

2

$\dfrac{3}{2} \in Q$ 

$\dfrac{2}{3} \in Z$

$ - \dfrac{9}{2} \notin Q$

$ - \;6 \in N$

\(\frac{5}{{ - 20}};\frac{{ - 5}}{{17}};\frac{1}{{ - 3}};\frac{{ - 7}}{{20}}\)

\(\frac{{ - 7}}{{20}};\frac{5}{{ - 20}};\frac{{ - 5}}{{17}};\frac{1}{{ - 3}}\)

\(\frac{{ - 7}}{{20}};\frac{1}{{ - 3}};\frac{{ - 5}}{{17}};\frac{5}{{ - 20}}\)

\(\frac{1}{{ - 3}};\frac{{ - 5}}{{17}};\frac{5}{{ - 20}};\frac{{ - 7}}{{20}}\)

$\dfrac{{ - 2}}{{ - 3}}$

$\dfrac{{ - \,2}}{5}$

$\dfrac{{ - \,5}}{{15}}$

$\dfrac{2}{{ - 15}}$