equationsmath-modeparagraphs
Let's say I have a text block like this:
Within the field of texture analysis, a number of categories of
methods exist, and even if we restrict ourselves to statistical
methods, a large number of methods are available.\begin{equation}Statistical approaches are considered to
f(x) = x + 3 \end{equation}
be generally applicable and work well for natural textures present in
images.
Here the \begin{equation} f(x) = x + 3 \end{equation} won't work. Could someone please help me?
You do not say what you expect \mathrm to do however it switches to the roman font font specified by the math version in use, which is what your images show.
You will see the difference between \text (which switches to the current text font) and \textnormal (which switches to the document default font) if you test it at a point where the current text font is not the default.
\math.... commands are math mode commands which switch the font used for letters but the content is processed in math mode. \text... commands are text mode commands which process their content in text mode, they are also allowed in math but process the commands in an hbox (by default) or if amsmath is loaded they use \text internally so that they switch to smaller sizes in subscripts etc, however the setting is still in an hbox, so that the content is processed as text rather than math.
\documentclass{article}
\usepackage{amsmath}
\begin{document}
abcdef
$\text{abcdef} + \textrm{abcdef} + \textnormal{abcdef} + \mathrm{abcdef}$
{\sffamily
abcdef
$\text{abcdef} + \textrm{abcdef} + \textnormal{abcdef} + \mathrm{abcdef}$
}
\end{document}
When defining operators you should really use \DeclareMathOperator and not directly use font commands at all, then it works as you wish in beamer, giving sans serif. If you have existing expressions using \mathrm and you want \mathrm to behave like \mathsf in beamer` you can redefine it as shown in the second expression below.
\documentclass{beamer}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\DeclareMathOperator\mycos{cos}
\begin{document}
\begin{frame}
$
\cos 1
\mathop{\mathrm{cos}} 2
\mycos 3
\operatorname{cos}4
\mathop{\mathsf{cos}}
$
\let\mathrm\mathsf
$
\cos 1
\mathop{\mathrm{cos}} 2
\mycos 3
\operatorname{cos}4
\mathop{\mathsf{cos}}
$
\end{frame}
\end{document}
Probably you like to achieve this:
Instead of \text in first occasion you should use \parbox which enable to write two line text. After than you need to clean-up remedy with curly braces:
\begin{document} %starts document
\begin{align} %starts a formula block
\parbox{8.5em}{Number of looks in\\ azimuth direction}
&= \frac{\text{Pixel spacing slant range}}
{\text{Pixel spacing azimuth}}\times \sin (\text{Incidence angle})\\
&= \frac{9.3685143}{3.5448059\times \sin (23.871^\circ)}
\end{align} %ends formula block
\end{document}
Addendum:
Considering Andrew Swann comment, use siunitx for units and make text width a bit wider with geometry package I obtain:
\documentclass[a4paper,11pt]{article}
\usepackage[showframe]{geometry} % show page layout and make text width wider ...
% in final use option "showframe" had to be removed
\usepackage{amsmath} % declares a predefined package for math
\usepackage{siunitx}
\begin{document} %starts document
\begin{align} %starts a formula block
\parbox{8.3em}{\centering Number of looks in\\ azimuth direction}
&= \frac{\text{Pixel spacing slant range}}
{\text{Pixel spacing azimuth}\times \sin (\text{Incidence angle})}\\[1ex]
&= \frac{9.3685143}{3.5448059\times \sin (\SI{23.871}{\degree})}
\end{align} %ends formula block
\end{document}
Edit:
It seems that factor \sin{...} had to be in the denominator. I correct this my misunderstanding of given MWE. Above mine MWE and image of equation is now corrected.
Best Answer
Use dollar symbols:
Note that equations should be part of a sentence. Also, you might like to read the Not So Short Introcution to LaTeX2e.