Tìm x, biết: a) (frac{1}{5}:x = frac{1}{5} + frac{1}{7})b) (frac{{x - 1}}{9} = frac{8}{3})c) (frac{5}{{16}}:x - frac{1}

* Hướng dẫn giải

a) \(\frac{1}{5}:x = \frac{1}{5} + \frac{1}{7}\)

\(\begin{array}{l}
\frac{1}{5}:x = \frac{{12}}{{35}}\\
x = \frac{1}{5}:\frac{{12}}{{35}}\\
x = \frac{7}{{12}}
\end{array}\)

b) \(\frac{{x - 1}}{9} = \frac{8}{3}\)

\(\frac{{x - 1}}{9} = \frac{{24}}{9}\)

Suy ra x - 1 = 24 => x = 25

c) \(\frac{5}{{16}}:x - \frac{1}{4} = \frac{5}{{12}}\)

\(\begin{array}{l}
\frac{5}{{16}}:x = \frac{5}{{12}} + \frac{1}{4}\\
\frac{5}{{16}}:x = \frac{2}{3}\\
x = \frac{5}{{16}}:\frac{2}{3}\\
x = \frac{{15}}{{32}}
\end{array}\)