title: Can you do addition/multiplication with Big O notations?
body: <p>I'm currently taking an algorithm class, and we're covering Big O notations and such. Last time, we talked about how</p>
  
  <pre><code>O (n^2 + 3n + 5) = O(n^2)
  </code></pre>
  
  <p>And I was wondering, if the same rules apply to this:</p>
  
  <pre><code>O(n^2) + O(3n) + O(5) = O(n^2)
  </code></pre>
  
  <p>Also, do the following notations hold ?</p>
  
  <pre><code>O(n^2) + n
  </code></pre>
  
  <p>or</p>
  
  <pre><code>O(n^2) + Θ (3n+5)
  </code></pre>
  
  <p>The later n is outside of O, so I'm not sure what it should mean. And in the second notation, I'm adding O and Θ .</p>