title: R print equation of linear regression on the plot itself
body: <p>How do we print the equation of a line on a plot?</p>
  
  <p>I have 2 independent variables and would like an equation like this:</p>
  
  <pre><code>y=mx1+bx2+c
  
  where x1=cost, x2 =targeting
  </code></pre>
  
  <p>I can plot the best fit line but how do i print the equation on the plot?</p>
  
  <p>Maybe i cant print the 2 independent variables in one equation but how do i do it for say 
  <code>y=mx1+c</code> at least?</p>
  
  <p>Here is my code:</p>
  
  <pre><code>fit=lm(Signups ~ cost + targeting)
  plot(cost, Signups, xlab="cost", ylab="Signups", main="Signups")
  abline(lm(Signups ~ cost))
  </code></pre>