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Show that the set of irrational numbers is an uncountable set.

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To proof: Set of irrational numbers RQ\bold{R}-\bold{Q} is uncountable.

PROOF BY CONTRADICTION\textbf{PROOF BY CONTRADICTION}

The set of real numbers R\bold{R} is uncountable.

The set of rational numbers Q\bold{Q} is uncountable.

The set of irrational numbers RQ\bold{R}-\bold{Q} is the set of real numbers without all rational numbers. The set of real numbers is then the union of the irrational and rational numbers:

R=(RQ)Q\bold{R}=(\bold{R}-\bold{Q})\cup \bold{Q}

Let us assume that RQ\bold{R}-\bold{Q} is countable. Since the union is two countable sets is also countable, we then obtain that R\bold{R} is countable. However R\bold{R} is known to be uncountable and thus we obtained a contradiction. Thus are assumption that RQ\bold{R}-\bold{Q} is countable is incorrect and thus RQ\bold{R}-\bold{Q} is uncountable.

\square

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