documentclass[leqno, fleqn,12pt]{article}
usepackage{mathtools}
usepackage{xfrac}
usepackage{multicol}

begin{document}

section*{List of Common Derivatives}
subsection*{POLYNOMIAL FUNCTIONS}

begin{multicols}{3}

begin{equation*}
frac{d}{dx} left(cright) = 0 %,where c is a constant
end{equation*}

begin{equation*}
frac{d}{dx} left(cxright) = c
end{equation*}

begin{equation*}
frac{d}{du} left(u^nright) = nu^{n-1}du
end{equation*}

end{multicols}

end{document}