1. The problem statement, all variables and given/known data a. How do I write vectors bold within displaymath and frac. I want Phi, r and r_1 bold. But get G M_1 bold as well = bad. b. How do I use arrows instead of the bold notation? 3. The attempt at a solution \begin{displaymath} a1. textbf{\Phi(r)} = -\frac{G M_1}{| textbf{r}-textbf{r_1} |} \end{displaymath} a2. \bf{\Phi}(\bf{r}) = -\frac{G M_1}{| \bf{r}-\bf{r_1} |}
Arrows: \vec : [tex]\vec \Phi ( \vec r) = -\frac{G M_1}{| \vec{r}-\vec r_1 |} [/tex] Bold: \mathbf : [tex]\mathbf{\Phi}( \mathbf{r}) = -\frac{G M_1}{| \mathbf{r}-\mathbf{r_1} |} [/tex] I don't think you really want the potential to be a vector, but that's what your code implied, so I kept it.
You get other bad stuff as well using \textbf. Don't use it in math mode. \textbf{\Phi(r)} = -\frac{G M_1}{| \textbf{r}-\textbf{r_1} |} [tex]\textbf{\Phi(r)} = -\frac{G M_1}{| \textbf{r}-\textbf{r_1} |}[/tex] \bf doesn't work at all: \bf{\Phi}(\bf{r}) = -\frac{G M_1}{| \bf{r}-\bf{r_1} |} [tex]\bf{\Phi}(\bf{r}) = -\frac{G M_1}{| \bf{r}-\bf{r_1} |}[/tex] Timo suggested \mathbf, but that doesn't work on some things. If you have access to the AMSLaTeX macros, (and you should), use \boldsymbol. \boldsymbol{\Phi}(\boldsymbol{r}) = -\frac{G M_1}{| \boldsymbol{r}-\boldsymbol{r}_1 |} [tex]\boldsymbol{\Phi}(\boldsymbol{r}) = -\frac{G M_1}{| \boldsymbol{r}-\boldsymbol{r}_1 |}[/tex] Use \vec. An even better solution is to define your own vector macro that formats vectors the way you want them to appear. For example, \newcommand{\vect}[1]{\boldsymbol{#1}} Then when someone tells you to format your vectors with arrows instead you can simply change that one macro. \newcommand{\vect}[1]{\vec{#1}}Bold symbols are used for things other than vectors (matrices, for example). A global search-and-replace is not a good idea.