title: R: Add a curve,with my own equation, to an x,y scatterplot
body: <p>I want to add a curve with the following equation to an x,y scatterplot: 
  y&lt;-(105+0.043(x^2-54x)). Is it possible within the plot() function? Also, if I use qplot instead (ggplot2) is there a way to draw this curve?</p>