title: R: Unable to do linear regression using square of a feature
body: <p>I have code below using the build-in dataset <code>mtcars</code>:</p>
  <pre><code>data(mtcars)
  model_1 &lt;- lm(mpg ~ wt + log(wt), data = mtcars)
  summary(model_1)
  
  model_2 &lt;- lm(mpg ~ wt + wt^2, data = mtcars)
  summary(model_2)
  </code></pre>
  <p>In <code>model_1</code>, things work well and I have two features <code>wt</code> and <code>log(wt)</code> in my regression result.</p>
  <p>But in <code>model_2</code>, I only have <code>wt</code> in the result, and I don't have the square of <code>wt</code>. Why and how to fix?</p>