# Math Help - Finite Set

1. ## Finite Set

Let U be a finite set and V a subset of U.

Prove that |U \ V| = |U| - |V|

I can see this in my head and if i draw a picture but how do i prove it? thanks for any help

2. Take note of two facts:
$U = \left( {U\backslash V} \right) \cup V\;\& \;A \cap B = \emptyset \; \Rightarrow \;\left| {A \cup B} \right| = \left| A \right| + \left| B \right|$