diff --git a/chapters/functions.tex b/chapters/functions.tex
index 05dc82c86..4e169e122 100644
--- a/chapters/functions.tex
+++ b/chapters/functions.tex
@@ -1470,7 +1470,7 @@ \subsection{Using the Derivative Annotation}\label{using-the-derivative-annotati
 \begin{eqnarray*}
 \frac{d}{dt}fg(x(t))&=&\frac{d}{dt}f(x(t),g(x(t)))\\
 &=&\frac{\partial f}{\partial x}\frac{dx}{dt}+\frac{\partial f}{\partial y}\frac{\partial g}{\partial x}\frac{dx}{dt}\\
-&=&(\frac{\partial f}{\partial x}+\frac{\partial f}{\partial y}\frac{\partial g}{\partial x})\frac{dx}{dt}\\
+&=&\left(\frac{\partial f}{\partial x}+\frac{\partial f}{\partial y}\frac{\partial g}{\partial x}\right)\frac{dx}{dt}\\
 &=&\textrm{f\_der}(x,y)\frac{dx}{dt}
 \end{eqnarray*}
 \end{nonnormative}