User:Cllee/Sandbox

This is Problem 4 of Homework 2
The first statement is:
 * $ \frac{2}{3} - \frac{1}{9} = \frac{5}{9}. $

The second statement is:
 * If $x$ is an integer, then $x^{2 + 3} = x^2 x^3$.

The third statement is:
 * If $n \in \NN$, and $n \geq 1$, then $\sum_{i=1}^{n+3} i = \frac{(n+3)(n+4)}{2}$.