In the mathematical formula, there are three commands \mathbf, \boldsymbol and \bm that can be used for bold operation, but \mathbf cannot be used for bold Greek letters. You can use the last two commands separately: \usepackage{amsmath} and \usepackage{bm}.

The following example:

\documentclass{article}

\ Title {\ LaTeX {and ZhiDao}

\ Date {2065 1 Month 438 +08}

\usepackage{amsmath}

\usepackage{bm}

\ begin {document}

\ Make a title

\begin{align}

\mathbf{Acd}=Acd \\

\mathbf{\alpha}=\alpha \\

\boldsymbol{\sigma}=\sigma \\

\bm{\beta}=\beta

\end{align}

\end{document}

The output result is:

You can see that 1, 3, 4 are not bold, and 2 is not bold. You cannot adjust the code box, which is represented by a list. Just remove the previous numbers.