title: Annotate exponential function ggplot2
body: <p>I would just like to simply add an annotation to my ggplot with the exponential function on it like this graph:
  <a href="https://i.stack.imgur.com/pdzRz.jpg" rel="nofollow noreferrer">excel graph</a></p>
  
  <p>Here is the data:<a href="https://i.stack.imgur.com/tdCYs.jpg" rel="nofollow noreferrer">Data</a></p>
  
  <p>Here is the code I used thus far:</p>
  
  <pre><code>dfplot&lt;-ggplot(data, aes(dilution.factor,Concentation)) + 
  geom_point(size=3)+ geom_smooth(method="auto",se=FALSE, colour="black")+
  scale_y_continuous(breaks=seq(0,14,by=2))
  
  dfplot2&lt;-dfplot+labs(x=('Dilution Factor'), y=expression('Concentration' ~ 
  (ng/mu*L)))+
  theme_bw() + theme(panel.border = element_blank(),
                   panel.grid.major = element_blank(),
                   panel.grid.minor = element_blank(),
                   axis.text = element_text(colour="black"), 
                   axis.line = element_line(colour = "black"))
  
  dfplot3&lt;- dfplot2+annotate("text", x=3, y=10, label = "R^2 == 1",parse=TRUE)
  dfplot3
  dfplot4&lt;-dfplot3+annotate("text", x=3, y=11, label = 
  as.character(expression("y=13.048e^-{0.697x}" ,parse=TRUE)))
  dfplot4
  </code></pre>
  
  <p>I can get all the way up to putting the r^2 value (dfplot3)<a href="https://i.stack.imgur.com/eu2xe.jpg" rel="nofollow noreferrer">dfplot3</a>
  For some reason I cannot get it to add the exponential equation in. I keep getting this error: 
  Error: Aesthetics must be either length 1 or the same as the data (1): label</p>
  
  <p>What am i doing wrong? </p>