LaTeX測試

$\LaTeX$
$\LaTeX$
$$\LaTeX$$
$$\LaTeX$$
$$\frac{1}{2}$$ $\frac{1}{2}$
${\frac{-b \pm \sqrt{b^2 - 4ac}}{2a}}$
$x = {-b \pm \sqrt{b^2-4ac} \over 2a}$