title: How to understand big O, big omega and big theta statement?
body: <p>There is a question:</p>
  <blockquote>
  <p>Which one of the following statements is TRUE?</p>
  <p>A 15n^2 + 3n + 2 E O(n log2 n)</p>
  <p>B. 15n^2 + 3n + 2 E n(n4)</p>
  <p>C. 15n^2 + 3n + 2 E O(n3 )</p>
  <p>D. 15n^2 + 3n + 2 E 0(15)</p>
  </blockquote>
  <p>Some symbol is not shown correctly, hence I upload a screenshot for this</p>
  <p><a href="https://i.stack.imgur.com/YYgee.png" rel="nofollow noreferrer">screentshot of question</a></p>
  <p>I put all statement into graph as shown below:</p>
  <p><a href="https://i.stack.imgur.com/OqnJI.png" rel="nofollow noreferrer">graph of statements</a></p>
  <p>I still can not figure out which is correct answer, 15n^2 + 3n + 2 is a sub-set for all option, I might misunderstand some definition, but I tried to search lots of, and I can not get any idea, can anyone help me, thanks!!!!!</p>