title: Two's Complement, subtracting two negative binary numbers
body: <p>So I'm doing CS and the lecturer wrote out a new binary question that I can't wrap my head around.</p>
  
  <p>Basically, how do you subtract two negative numbers if they are in binary? </p>
  
  <p>Specifically how to do it using Two's Constant which was just introduced. </p>
  
  <p>For example: <code>-2 - -7 = 5</code><br>
  Or: <code>1110 - 1001</code></p>
  
  <p>I don't understand how you use those bits to get the correct answer, I.e. 5.</p>
  
  <p>Can anyone help please?</p>