How to make the bar for simplify

Question

How can i write the bar/slash over the m in latex?

Answer 1

You can use the slashed package.

\documentclass[a4paper,12pt]{article}
\usepackage{mathtools,slashed}
\begin{document}
$P_0(\slashed{m} \frac{t\lambda}{\slashed{m}})$
\end{document}

Using Latex to write math equations is easy but overwhelming at the beginning. Maybe you find Detexify or Mathpix useful when you can write down what you need but do not have the words to describe it clearly.

Answer 2

Using \not command.

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amssymb}
\begin{document}
[P_0\left(\not m \frac{\lambda t}{\not m}\right)]
\end{document}