latex double integral code example

Example 1: latex sum

Inside text: $\sum_{n=1}^{\infty} 2^{-n} = 1$
On its own line: $$\sum_{n=1}^{\infty} 2^{-n} = 1$$

Example 2: limit in latex

$\lim_{x\to\infty} f(x)$

Example 3: integral latex

$\int_0^{2a}{\cos(x)dx}$