Make displaystyle equations larger

Question

This is my first time with this markup language, and it looks like my question has already been asked and answered, but when I try to apply those solutions, they do not work (I assume because I'm using a displaystyle command, but if I do not use that command then the equations don't render!).

I want to render a set of 2 partial differential equations in a large font size, but all I can seem to get is size 10.

Here's my code and the resulting image.

\documentclass{article}

\begin{document}

{\displaystyle { {\dot {q}}=+H_{p}}

{\displaystyle { {\dot {p}}=-H_{q}}

\end{document}

Answer 1

Here is the code that I suppose can do what you want:

\documentclass{article}
\usepackage{anyfontsize}

\begin{document}
\fontsize{15}{18}\selectfont
$\displaystyle \dot{q}=+H_{p}$

$\displaystyle \dot {p}=-H_{q}$

\end{document}

Be carefull:

1. You don't need so much brackets ({ and }).
2. Math code must included in $ my-math-here $ (for inline math) or in $$my-math-here$$ if you want your math to have their own line or better \[my-math-here\] (same as before with own line). Also are options like \begin{equation} my-math-here \end{equation} that gives enumerated equations.
3. The basic fontsize of your document is been given in documentclass command like \documentclass[12pt]{article} and then you have commands to change it inside your document like \small, \Huge, \footnotesize etc (search for 'latex fontsizes'). But if they are not enough you can use anyfontsize package.
4. Especially for math sizes take a look here: Make equations large