# Reduce font size only for all display equations [duplicate]

Is this possible to reduce the fontsize for display equations smaller than the normal text font size. I'm using the following tags:

\documentclass[10pt]{book}
\usepackage{amsmath}
\begin{document}

This is for test
\beign{align}
a+b=c
\end{align}

\begin{gather}
a+b=c
\end{gather}

All amsmath environments follows...
\end{document}


Giving each equations \small is a tedious way...

• Please tell us more about what you're ultimately trying to achieve. Depending on what these goals may be, there may be better ways to achieve the goals than by reducing the font size employed in display-math material. – Mico Aug 1 '18 at 6:51
• @Mico One of my known person approaching me to write his thesis in LaTeX, it having some large equations, so he decided to reduce all the display math font size smaller than the text size. He is using many amsmath environments like align, gather, subequations, etc. He tried to decrease the font size manually each an every equations, but it takes huge time, can you advise ? – MadyYuvi Aug 1 '18 at 7:08
• I would not reduce the font size used in math material. Instead, I'd reduce the values of \abovedisplayskip and \belowdisplayskip (can you guess what these parameters control?), I'd check that the setspace package is loaded properly and with the option nodisplayskipstretch, and I'd make sure that the displaymath enviroments are used correctly, by which I mean, in a manner that doesn't create excessive whitespace. In comparison with these three methods, the vertical space one could save by reducing the font size is pretty much negligible. – Mico Aug 1 '18 at 7:38
• It would be helpful if you augmented your posting with some representative code produced by this "known person". What's the document's main font size? Which font families are in use? What's the height and width of the text block? Has the person loaded the setspace package (hopefully with the option nodisplayskipstretch), or has he/she modified low-level parameters such as \baselineskip directly? Does the person use \left and \right to autosize "fences", likely making the fences (and thus the equations too) taller than is necessary, let alone typographically correct? Please advise. – Mico Aug 1 '18 at 7:48
• it is not kind to the reader to use \small too often. But the main problem with your posted document is that it produces the error ! Undefined control sequence. l.6 \beign – David Carlisle Aug 1 '18 at 11:49