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Description $\LaTeX$ Symbol
Natural numbers \ mathbb{N} $\mathbb{N}$
Integer numbers \ mathbb{Z} $\mathbb{Z}$
Rational numbers \ mathbb{Q} $\mathbb{Q}$
Realnumbers \ mathbb{R} $\mathbb{R}$
Infinity \ infty $\infty$
Set Union \ cup $\cup$
Set Intesertion \ cap $\cap$
\ mid $\mid$
plus minus \ pm $\pm$
fraction \ frac{a}{b} \(\frac{a}{b}\)
fraction double size \ dfrac{a}{b} \(\dfrac{a}{b}\)
power a^b $a^b$
square root \ sqrt{a} $\sqrt{a}$
n root \ sqrt[b]{a} $\sqrt[b]{1}$
belongs, is an element of \ in $\in$
not belongs, isn’t an element of \ not \ in $\not\in$
not equal \ neq $a \neq 0$
Line segment \ overline{AB} $\overline{AB}$

Examples
x=\ frac{-b \ pm\ sqrt{b^2 + 4ac}}{2a} \[ x=\frac{-b \pm\sqrt{b^2 + 4ac}}{2a} \]
f(x) = \ left \ { \ begin{array}{lr} g(x) \\ t(x) \\ …\ end{array} \ right \ } $f(x) = \left\{ \begin{array}{lr} g(x) \\ t(x) \\ ...\end{array}\right\}$