The LaTeX command for dot deriv (ẋ) is \dot{x} (first time derivative (Newton notation)).
\dot{x}Writing a paper? The table generator and the BibTeX cleaner are one click away, no account.
Write \dot{x} inside math mode, that is between $…$ for inline math or in a \[ … \] or equation block for display math. It is part of core LaTeX math, so no extra package is required.
The physics and siunitx packages offer shortcuts for many formulas, but \dot{x} works in plain LaTeX. With unicode-math under XeLaTeX or LuaLaTeX, typing ẋ in a formula gives the same symbol.
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\dagger\hbar\nabla\nabla^2\nabla \cdot\nabla \times\partial\ddot{x}\langle \psi || \psi \rangle\langle \phi | \psi \rangle\rightleftharpoons\text{\AA}^\circ\mathrm{C}Physics symbols in LaTeX: the full table or search all 350+ LaTeX symbols.
Use \dot{x} in math mode; it needs no extra package. For example, $\dot{x}$.
None: \dot{x} is built into LaTeX, so no extra package is required.