# What is this math font?

I designated "D" on the image.

What is this math font called?

.

• It's just sans-serif. Try \mathsf{D}? – Au101 Dec 29 '16 at 4:14
• Thanks! Then how about to make it bold? I tried \mathbf{\mathsf{D}} , but it does not works. – Jay Lee Dec 29 '16 at 4:23
• Computer Modern does not have a bold sans-serif face, you will have to select a font that does have such a face – Au101 Dec 29 '16 at 4:24
• Also unlike text font commands \mathxx fonts do not combine so you would need to declare a new math alphabet for bold sans not use \mathbf{\mathsf – David Carlisle Dec 29 '16 at 17:18

You can either define your own math alphabet (here \mathbfsf) for bold sans-serif

\documentclass{article}
\DeclareMathAlphabet{\mathbfsf}{OT1}{cmss}{bx}{n}
\begin{document}

$\mathsf{D}$ $\mathbfsf{D}$

\end{document}


or you can use the bm package

\documentclass{article}
\usepackage{bm}
\begin{document}

$\mathsf{D}$ $\bm{\mathsf{D}}$

\end{document}


The output is in both cases