How do I write this in Latex. I've looked everywhere and to be honest I don't even know how to describe it in google search bar.
I have
$$(\frac{\partial u}{\partial t})_(t=0)$$
but it's the last part that does work properly
How do I write this in Latex. I've looked everywhere and to be honest I don't even know how to describe it in google search bar.
I have
$$(\frac{\partial u}{\partial t})_(t=0)$$
but it's the last part that does work properly
The underscore character (_) will make only one math atom a subscript. In the case of your code, it was the (. To make it work you have to group the t=0 using braces ({...}).
Also, use \left( and \right) instead of just ( and ) to make the parentheses taller for the fraction.
Finally, use \[ and \] to delimit the display math instead of $$ (reference).
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[\left(\frac{\partial u}{\partial t}\right)_{t=0}\]
\end{document}
I suggest using a dedicated package like esdiff to simplify typing. It defined a \diffp{function}{variables} command. In addition, the order of crossed partial derivatives is automatically calculated. The evaluation point of partial derivatives is added in the \diffp* command:
\documentclass{article}%
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{fourier}
\usepackage[thinc]{esdiff}
\begin{document}
\[ \diffp*{u}{t}{t = 0}\qquad \diffp{u}{t x}\qquad \diffp{u}{{t^2} x}\]%
\end{document}
$$ .. $$for display math, see Why is\[ … \]preferable to$$? – Torbjørn T. Mar 08 '18 at 12:23_{t=0}instead of_(t=0). – Bobyandbob Mar 08 '18 at 12:25