\[ f(x) = \left\{ \begin{array}{cl} x, & x \le 0 \\ \sin(x), & x > 0 \end{array} \right. \]

\[ (f \circ g)(x) = f(g(x)) \]

\[ \lim_{x \to x_0} f(x) = f(x_0) \]

\[ f(x) = \frac{p(x)}{q(x)} \]

\[ \lim_{n \to \infty} \frac{1}{n} = 0 \]

\[ p(x) = \sum_{k=0}^n a_kx^k \]