Tìm số hữu tỉ x trong các tỉ lệ thức sau: a)(1/5)x:3 = 2/3:0,25; b) - 3/8 =6/(4x - 2);

. a) \(\frac{1}{5}x:3 = \frac{2}{3}:0,25\)                                   

\(\frac{1}{5}x = \frac{{\frac{2}{3}\,\,.\,\,3}}{{0,25}}\)

\(\frac{1}{5}x = \frac{2}{{0,25}}\)

\(\frac{1}{5}x = 8\)

\(x = 40\).

Vậy \(x = 40\).

b) \(\frac{{ - 3}}{8} = \frac{6}{{4x - 2}}\)

\[4x - 2 = \frac{{6\,\,.\,\,8}}{{ - 3}}\]

\[4x - 2 =  - 16\]

\[4x =  - 16 + 2\]

\[4x =  - 14\]

\[x = \frac{{ - 7}}{2}\].

Vậy \[x = \frac{{ - 7}}{2}\].

b) \(\frac{{27}}{4} = \frac{3}{{{x^2}}}\)

\({x^2} = \frac{{3\,\,.\,\,4}}{{27}}\)

\({x^2} = \frac{4}{9}\)

\[{x^2} = {\left( { \pm \frac{2}{3}} \right)^2}\]

\[x =  \pm \frac{2}{3}\].

Vậy \[x =  \pm \frac{2}{3}\].