# Homework Help: The cardinality of the set of irrational numbers

1. Mar 15, 2012

### julypraise

1. The problem statement, all variables and given/known data
Suppose $\mathbb{Q},\mathbb{R}$ are the set of all rational numbers and the set of all real numbers, respectively. Then what is $|\mathbb{R} \backslash \mathbb{Q}|$?

2. Relevant equations
$|\mathbb{Q}| = |\mathbb{Z^{+}}| < |P(\mathbb{Z^{+}})| = |\mathbb{R}|$

3. The attempt at a solution
I can prove the relevant equations by the method of cut and general concepts of functions and logic. But actually my understanding of cut construction for R is kinda poor. So should I revise this concept to know the cardinality of the set of irrational numbers? Or do I need to know extra stuff?