{latex}
\large\[
\operatorname{Re}  = \frac{{4Q}}
{{\pi D\nu }}
\]
{latex}

\[
{\text{f}} = \frac{{0.25}}
{{\left[ {\log \left( {\frac{\varepsilon }
{{3.7D}} + \frac{{5.74}}
{{\operatorname{Re} ^{0.9} }}} \right)} \right]^2 }}
\]