Tìm số hữu tỉ x trong các tỉ lệ thức sau: a) 36/x = 54/3; b) (2x - 3)/4 =(x + 1)/7;

a) \(\frac{{36}}{x} = \frac{{54}}{3}\)                                         

\(x = \frac{{36\,\,.\,\,3}}{{54}}\)

\(x = 2\).

Vậy \(x = 2\).

b) \(\frac{{2x - 3}}{4} = \frac{{x + 1}}{7}\)

  \(7\,\,.\,\,\left( {2x - 3} \right) = 4\,\,.\,\,\left( {x + 1} \right)\)

  \(14x - 21 = 4x + 4\)

   \(10x = 25\)

        \(x = \frac{5}{2}\)

Vậy \(x = \frac{5}{2}\).

c) \(\frac{3}{{{x^2} - 2}} = \frac{2}{6}\)

\({x^2} - 2 = \frac{{3\,\,.\,\,6}}{2}\)

\({x^2} - 2 = 9\)

\({x^2} = 11\)

\(x =  \pm \sqrt {11} \).

Vậy \(x =  \pm \sqrt {11} \).