\documentclass[10pt,letterpaper]{article}
\usepackage[latin1]{inputenc}
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\author{Charles Edward Pax}
\begin{document}
\center
$V_F = \pi\left(\frac{D_F}{2}\right)^2v_F$

$V_F = \frac{\pi}{4}D_F^2v_F$

$V_E = \pi\left(\frac{D_E}{2}\right)^2v_E$

$V_E = \frac{\pi}{4}D_E^2v_E$

$V_E = V_F$

$\frac{\pi}{4}D_E^2v_E = \frac{\pi}{4}D_F^2v_F$

$v_E = \frac{D_F^2v_F}{D_E^2}$

$v_F = \frac{D_P}{2}2\pi f$

$v_F = \pi D_pf$

$V_E = \frac{D_F^2\pi D_Pf}{D_E^2}$

\end{document}