Increase the fontsize on either the whole document or just a segment

Question

How do you increase the fontsize on either the whole document or preferably just this segment?

 \begin{center}
       $R_{ecl} = \sqrt{(X_{ecl}^{2} + Y_{ecl}^{2} + Z_{ecl}^{2})}$\\
       $\lambda = \arctan{\frac{Y_{ecl}}{X_{ecl}}}$\\
       $\beta = \arctan{\frac{Z_{ecl}}{\sqrt{(X_{ecl}^{2} + Y_{ecl}^{2})}}}$\\
 \end{center}

Answer 1

For example

 \begin{center}
 \large
       $R_{ecl} = \sqrt{(X_{ecl}^{2} + Y_{ecl}^{2} + Z_{ecl}^{2})}$\\
       $\lambda = \arctan{\frac{Y_{ecl}}{X_{ecl}}}$\\
       $\beta = \arctan{\frac{Z_{ecl}}{\sqrt{(X_{ecl}^{2} + Y_{ecl}^{2})}}}$\\
 \end{center}

There is also \Large, \LARGE, \huge and \Huge.

Answer 2

Assuming you're using pdfLaTeX, you should primarily be looking at the commands \large, \Large, and \huge. Each command represents a 20% step-up in font size from the preceding level. To localize the effect of the font size change, place the macros either in a pre-defined environment (such as center) or encase them in a pair of \begingroup and \endgroup statements.

\documentclass{article}
\usepackage[vmargin=1cm]{geometry}
\usepackage{amsmath} % for "gather*" environment
\newcommand\threelines{\par
\begin{gather*}
       R_{ecl} = \sqrt{X_{ecl}^{2} + Y_{ecl}^{2} + Z_{ecl}^{2}}\\
       \lambda = \arctan{\frac{Y_{ecl}}{X_{ecl}}}\\
       \beta = \arctan{\frac{Z_{ecl}}{\sqrt{X_{ecl}^{2} + Y_{ecl}^{2}}}}
\end{gather*}}
\begin{document}

\verb+default font size+
\threelines

\begingroup
\large
\verb+20% larger+
\threelines
\endgroup

\begingroup
\Large
\verb+44% larger+
\threelines
\endgroup

\begingroup
\Huge
\verb+73% larger+
\threelines
\endgroup

\end{document}