# How to unbold a section of a \boldmath or \boldsymbol?

I have some locally defined commands such as

\newcommand{\cosx}[1]{\color{blue}\boldsymbol \cos^{#1} x}


and I would like to be able to unbold some part of it. Is there a more elegant way to achieve this than by repeating the commands as in:

\newcommand{\cosx}[1]{{\color{blue}\boldsymbol \cos}^{#1} {\color{blue}\boldsymbol x}}


e.g. some way of wrapping the section to be formatted normally?

I saw this question, but I believe that issue is actually more complicated as it feeds a bolded symbol into a new command; moreover, the solutions presented are beyond my ability to generalize to other situations (i.e. my question could be generalized to 'how to exempt a section in math mode from formatting (bold, colour, font etc)?').

• \unboldmath, perhaps? – user31729 Feb 15 '17 at 21:02
• thanks, but this wouldn't work for the colours or fonts, & does not appear to work for the bold, either... – Rax Adaam Feb 15 '17 at 21:09
• \boldsymbol takes an argument so in your example it only applies to \cos how can you unbold only part of that? – David Carlisle Feb 15 '17 at 23:16
• the first command has the \boldsymbol apply to everything i.e. \cos^{#1} x; the 2nd is a hacked version showing the effect I was trying to achieve. – Rax Adaam Feb 16 '17 at 20:40

I think you want (not sure why)

\documentclass{article}
\usepackage{amsmath}
\usepackage{bm}
\usepackage{xcolor}

\DeclareMathOperator{\bcos}{\textcolor{blue}{\mathbf{cos}}}
\newcommand{\bx}{\textcolor{blue}{\bm{x}}}

\begin{document}

$\bcos^2\bx$

\end{document}


If you really want the \cosx macro, add

\newcommand{\cosx}[1]{\bcos^{#1}\bx}

• This achieves the desired effect (I am a teacher & do extensive colour-coding in my notes to help students follow steps and see the most important info), but seems to me a variation on what I posted. Is there nothing like \$\bm{\cos x \cdot \normalmath{\sin x} \cdot \cos x} = \cos^{\bm{2}}x \cdot \sin x where everything inside \normalmath{ } would be rendered in default font-style? – Rax Adaam Feb 16 '17 at 20:49
• & is there any reason to use \DeclareMathOperator{} over \newcommand for the blue / bold cos(x)? Would be interested to learn more if you can point me in the right direction. Thank you kindly for all your help! – Rax Adaam Feb 16 '17 at 20:50
• @RaxAdaam The main reason is that as an operator, the symbol gets the right spacing. – egreg Feb 16 '17 at 21:47
• thank you - that is enormously helpful to know & stands to simplify a lot of the local commands I've implemented. – Rax Adaam Feb 23 '17 at 20:42