title: Running time of algorithm A is at least O(n²) - Why is it meaningless?
body: <p>Why is the statement:</p>
  
  <blockquote>
    <p>The running time of algorithm A is at least O(n²)</p>
  </blockquote>
  
  <p>is meaningless ? </p>
  
  <blockquote>
    <p>The running time of Insertion sort algorithm is at most O(n²)</p>
  </blockquote>
  
  <p>Is it Correct?</p>
  
  <p>I tried the net but could not get a good explanation.</p>
  
  <p>I have another question:</p>
  
  <blockquote>
    <p>I know that any linear function a⋅n+b is O(n) and also O(n²). Is it also O(n³)?</p>
  </blockquote>