1.上下标: $x^n$, $x^{123}$, $x_n$, $x_{123}$, $C_n^m$, $C_{100}^{50}$ $x^n$, $x^{123}$, $x_n$, $x_{123}$, $C_n^m$, $C_{100}^{50}$ 2.花括号: $\{a_n\}$ $\{a_n\}$ 3.分式: $\frac{a}{b}$, $\frac12$, $\frac1{23}$ $\frac{a}{b}$, $\frac12$, $\frac1{23}$ 4.根式: $\sqrt