text: Q:
  
  Rmarkdown Beamer 16:9 aspect ratio
  
  How to set the aspect ratio of beamer slides created using Rmarkdown in Rstudio to 16:9? It does not seem to be a standard option. I tried changing the \documentclass{} options using a header.tex insert but this was not successful.
  
  A:
  
  Put the option in double quotes:
  output: 
    beamer_presentation:
  classoption: "aspectratio=169"
  
  Notice that classoption keyword is at the same level with output. 
  
  pandoc 1.19
  texlive 2015
  knitr 1.17
  rmarkdown 1.6
  
  