This is an example of an in-line equation: \( \frac{n!}{k!(n-k)!} = \binom{n}{k} \)
Each of the following two examples is a displayed equation (which means that the equation is placed on a new line and centered):
\[ \lim\limits_{x \to \infty} \exp(-x) = 0 \]
\[ \sum_{i=1}^{n}i = \frac{n(n+1)}{2} \]