$x_{a}$$x^{b}$$x_{a}^{b}$$\bar{x}$$\tilde{x}$$\frac{a}{b}$$\sqrt{x}$$\sqrt[n]{x}$$\bigcap_{a}^{b}$$\bigcup_{a}^{b}$$\prod_{a}^{b}$$\coprod_{a}^{b}$ $\left \{ x \right \}$ $\int_{a}^{b}$$\oint_{a}^{b}$$\sum_{a}^{b}{x}$$\lim_{a \rightarrow b}{x}$$ \begin{pmatrix}a&b\\c&d\\ \end{pmatrix}$$ \begin{bmatrix}a&b\\c&d\\ \end{bmatrix}$$\begin{Bmatrix}a&b\\c&d\\ \end{Bmatrix}$$\begin{vmatrix}a&b\\c&d\\ \end{vmatrix}$ $\lim_ {x \to 0}{x}$ $\lim_\limits{x \rightarrow 0}{x}$ 方程组 向量 $\overline x$ $\triangle ABC$ $\angle A$ $180^{\circ}$ $a \div b= \dfrac{a}{b}$ $\pm a$ $\because$ $\therefore$ $AB \perp CD$ $\angle ABC =\frac{1}{2} \overparen{DE}$ $\triangle \mathrm{ABC} \cong \triangle \mathrm{DEF}$ $\triangle ABC \sim \triangle DEF$ $\odot O$ $\square ABCD$ $y=\log _{a} x$ $\varnothing \subseteq A$ $A \cap B$ $A \cup B$ $k \in N$