title: How would I fit this linear trend function in R?
body: <p>I want to fit this linear trend function to my data: </p>
  
  <p>Y<sub>t</sub>=a+bt+X<sub>t</sub></p>
  
  <p>This is based on time series data.
  I believe writing <code>lm(y ~ time)</code> will return the equivalent of Y<sub>t</sub>=a+X<sub>t</sub> but I'm confused how to include bt into this linear trend function in R.</p>