\[f(x) = \frac{5x + 4}{4x^{2} - x}\text{\ \ }\]
\[4x^{2} - x \neq 0\]
\[x(4x - 1) \neq 0\]
\[x \neq 0;\ \ x \neq \frac{1}{4}\]
\[\Longrightarrow D(f) =\]
\[= ( - \infty;0) \cup \left( 0;\frac{1}{4} \right) \cup \left( \frac{1}{4}; + \infty \right).\]