1. The problem statement, all variables and given/known data http://img82.imageshack.us/img82/8125/78492134fy0.th.jpg [Broken]http://g.imageshack.us/thpix.php [Broken] I need to prove that the left part is equal to the right. I'm not sure how to approach the question. I know that (n over k)=n! : k!(n-k)! but how do I sum all the number from k=0 to k=n and show that that equals to 2^n ?