So i'm not sure at all how to prove things using a combinatorial proof. Where to do i start? What do i need to think about etc. For example how would i prove
$$\sum_{i=0}^n {n \choose i} 2^i = 3^n $$
So i'm not sure at all how to prove things using a combinatorial proof. Where to do i start? What do i need to think about etc. For example how would i prove
$$\sum_{i=0}^n {n \choose i} 2^i = 3^n $$