title: R knitr PDF problems with \includegraphics
body: <p>Using a new empty .rmd document, this code works: </p>
  
  <pre><code>![](RainbowDolphin.png)
  \begin{center}
  \includegraphics[width=4in]{RainbowDolphin.png}
  \end{center}
  </code></pre>
  
  <p>But without the first line, it doesn't: </p>
  
  <pre><code>\begin{center}
  \includegraphics[width=4in]{RainbowDolphin.png}
  \end{center}
  </code></pre>
  
  <p>I get an error:</p>
  
  <pre><code>! Undefined control sequence.
  l.71 \includegraphics
  
  pandoc.exe: Error producing PDF from TeX source
  Error: pandoc document conversion failed with error 43
  In addition: Warning message:
  running command '"C:/Program Files/RStudio/bin/pandoc/pandoc" Sampling_03.utf8.md --to latex --from markdown+autolink_bare_uris+ascii_identifiers+tex_math_single_backslash-implicit_figures --output Sampling_03.pdf --template "C:\PROGRA~1\R\R-31~1.2\library\RMARKD~1\rmd\latex\default.tex" --highlight-style tango --latex-engine pdflatex --variable "geometry:margin=1in"' had status 43 
  Execution halted
  </code></pre>
  
  <p>Weird. Any help appreciated!</p>