a) \(\dfrac{1}{2}< \dfrac{12}{a}< \dfrac{4}{3}\)
\(6\cdot\dfrac{1}{2}< 6\cdot\dfrac{12}{a}< 6\cdot\dfrac{4}{3}\)
\(3< \dfrac{72}{a}< 8\)
\(\dfrac{72}{3}>a>\dfrac{72}{8}\)
\(24>a>9\)
Vậy: ...
b) \(\dfrac{14}{5}< \dfrac{a}{5}< 4\)
\(\dfrac{14}{5}\times5< a< 5\times4\)
\(14< a< 20\)
a, \(\dfrac{1}{2}< \dfrac{12}{a}< \dfrac{4}{3}\Leftrightarrow\dfrac{1}{24}< \dfrac{1}{a}< \dfrac{1}{9}\Leftrightarrow9< a< 24\)
b, \(\dfrac{14}{5}< \dfrac{a}{5}< 4\Leftrightarrow14< a< 20\)
a) = 12/6 < 12/a < 12/9
a = 7; 8; 9
b) = 14/5 < a/5 < 20/5
a = 15; 16; 17; 18; 19
