How to boldify math equation and plain text simultaneously

Yo can apply \boldmath:

Surrounding it with {...} limits the scope to be just within the curly braces so subsequent text is not effected.

Notes:

• As per egreg's suggestion I have replaced $s=9, s*s$ with $s=9$, $s*s$. The , is not really part of the math, thus, it should be outside. This yields better spacing.

Code:

\documentclass{article}
\begin{document}
Since $s=9$, $s*s$ becomes 81

{\bfseries\boldmath Since $s=9$, $s*s$ becomes 81}

Since $s=9$, $s*s$ becomes 81

\end{document}

Run with lualatex or `xelatex

\documentclass{article} 
\usepackage{unicode-math}
\setmathfont{xits-math.otf}
\setmathfont[version=bold]{xits-mathbold.otf}
\newcommand\allBold[1]{{\bfseries\mathversion{bold}#1}}
\newcommand\allbold[1]{{\bfseries\boldmath#1}}
\begin{document}

Since $s=9, s*s$ becomes 81 $\displaystyle\int_a^b f(x)\mathrm{d}x$

\allbold{Since $s=9, s*s$ becomes 81 $\displaystyle\int_a^b f(x)\mathrm{d}x$}

\allBold{Since $s=9, s*s$ becomes 81 $\displaystyle\int_a^b f(x)\mathrm{d}x$}

Since $s=9, s*s$ becomes 81 $\displaystyle\int_a^b f(x)\mathrm{d}x$
\end{document}