KaTeX can be used to generate complex math formulas. It supports in-line math using the \\( ... \\) delimiters, like this: \( E = mc^2 \). By default, it does not support in-line delimiters $...$ because those occur too commonly in typical webpages. It supports displayed math using the $$ or \\[...\\] delimiters, like this:
Formula 1: $$ \phi = \frac{(1+\sqrt{5})}{2} = 1.6180339887\cdots $$
Formula 2: (same formula, different delimiter) \[ \phi = \frac{(1+\sqrt{5})}{2} = 1.6180339887\cdots \]
Additional details can be found on GitHub or on the Wiki.
Example 1
If the text between $$ contains newlines it will rendered in display mode:
$$
f(x) = \int_{-\infty}^\infty\hat f(\xi)\,e^{2 \pi i \xi x}\,d\xi
$$
$$ f(x) = \int_{-\infty}^\infty\hat f(\xi),e^{2 \pi i \xi x},d\xi $$
Example 2
$$
\frac{1}{\Bigl(\sqrt{\phi \sqrt{5}}-\phi\Bigr) e^{\frac25 \pi}} = 1+\frac{e^{-2\pi}} {1+\frac{e^{-4\pi}} {1+\frac{e^{-6\pi}} {1+\frac{e^{-8\pi}} {1+\cdots} } } }
$$
$$ \frac{1}{\Bigl(\sqrt{\phi \sqrt{5}}-\phi\Bigr) e^{\frac25 \pi}} = 1+\frac{e^{-2\pi}} {1+\frac{e^{-4\pi}} {1+\frac{e^{-6\pi}} {1+\frac{e^{-8\pi}} {1+\cdots} } } } $$
Example 3
$$
1 + \frac{q^2}{(1-q)}+\frac{q^6}{(1-q)(1-q^2)}+\cdots = \prod_{j=0}^{\infty}\frac{1}{(1-q^{5j+2})(1-q^{5j+3})}, \quad\quad \text{for }\lvert q\rvert<1.
$$
$$ 1 + \frac{q^2}{(1-q)}+\frac{q^6}{(1-q)(1-q^2)}+\cdots = \prod_{j=0}^{\infty}\frac{1}{(1-q^{5j+2})(1-q^{5j+3})}, \quad\quad \text{for }\lvert q\rvert<1. $$
Example 4
Remember, certain characters are rendered by markdown, so you may need to workaround those issues. You can find the complete list of KaTeX supported functions here: https://khan.github.io/KaTeX/docs/supported.html
For example, the ' character can be replaced with ^\prime:
$$ G^\prime = G - u $$
The " character can be replaced with ^{\prime\prime}:
$$ G^{\prime\prime} = G^\prime - v $$