Update chapters/functions.tex

Adjustable parenthesis

Co-authored-by: Elena Shmoylova <eshmoylova@users.noreply.github.com>

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}