This document discusses real numbers including the fundamental theorem of arithmetic, irrational numbers, and rational numbers and their decimal representations. It contains three sections: 1) The fundamental theorem of arithmetic states that every composite number can be uniquely expressed as a product of prime numbers. It also provides an example of using prime factorization to find the highest common factor and lowest common multiple of two numbers. 2) Irrational numbers like the square root of 2 are proven to be irrational by assuming they can be expressed as a ratio of integers and arriving at a contradiction. 3) Rational numbers with decimal representations that terminate can be expressed as a ratio of integers where the denominator is of a particular form. Other rational numbers have non-terminating