# How to write two dot above a letter?

the two dots above a letter represents two derivative of varible t.

My method:

\documentclass[UTF8]{ctexart}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{graphicx}
\usepackage{epstopdf}
\usepackage{inputenc}
$$\"{o} \mathaccent{o}$$


However,the latex says in the math environment ,I must use the \mathaccent. So I replace \" by \mathaccent, but it shows the warning information: Missing number, treated as zero

I am a starter, I want to know how to revise it? Can someone help me? Thanks sincerely!!

• Welcome to TeX.SE. Use $\dot x$ for the first derivative, \ddot x for the second, \dddot x for the third, \ddddot x for the fourth. – Peter Grill Jan 8 '14 at 3:03
• @Peter Grill,Thaks for your warm welcome and solution.I am a college student.I like Latex very much. – mma Jan 8 '14 at 3:08
• @ Peter Grill,Dear Peter Grill,BTW,how to write the "^" above a letter.\^{u} cannot achieve that effect in the math enviroment. – mma Jan 8 '14 at 3:27
• $\hat{u}$.... – user11232 Jan 8 '14 at 3:45
• I would like to extend this question and ask how one would do the same thing only under the letter or a word – tmwitten Jul 27 '15 at 5:00

The sequence

\"{o}


will be used when you want to write 'ö' in text, such as 'Schrödinger'. While in the math mode, as Peter Grill mentioned

\dot{o}
\ddot{o}


and so on, should do the trick.

Edit:

For more than two dots, e.g. \dddot{o}, you need the package amsmath, which allows you a maximum of 4 dots \ddddot{o} (not strikingly beautiful )

For higher dot derivatives take a look at this post