\documentclass{jarticle} \begin{document} $f(x) = x^2 + 2x -3$ \[ f(x) = x^2 + 2x - 3 \] \begin{equation} f(x) = ax^2 + bx + c \end{equation} \begin{eqnarray} ax^2 + bx + c & = & 0 \\ x & = & \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \end{eqnarray} \[ g(x) = \frac{x}{y} \] \[ y = \frac{1}{1 + \frac{1}{1 + x}} \] \[ \sqrt{2} + \sqrt[3]{5} \] \[ \sin{(\alpha + \beta)} = \sin{\alpha}\cos{\beta} + \cos{\alpha}\sin{\beta} \] \[ S_n = \sum_{k=1}^n ar^k \] \[ \int_{a}^{b}{x^2dx} = \left[{\frac{1}{3}x^3}\right]_{a}^{b} \] \[ \left( \begin{array}{lcr} x_{11} & \cdots & 1 \\ x_{21} & \cdots & 10 \\ \vdots & \ddots & \vdots \\ x_{n1} & \cdots & 100 \end{array} \right) \] \[ f(x) = \left\{ \begin{array}{ll} 1 & \mbox{ if $x = 0$, }\\ nf(n-1) & \mbox{ if $x \geq 1$ } \\ \end{array} \right. \] \end{document}