Formula blocks

Two dollar signs set the formula as a block of its own:

$$
\int_{-\infty}^{\infty} e^{-x^2} \, dx = \sqrt{\pi}
$$

$${\int }_{-\infty }^{\infty }{e}^{-x^2}dx=\sqrt{\pi }$$

Aligned over several lines

$$
\begin{aligned}
a &= b + c \\
  &= d + e + f \\
  &= g
\end{aligned}
$$

$$\begin{array}{rl}a& =b+c\\ & =d+e+f\\ & =g\end{array}$$

The & marks the place where the lines line up.

Matrices

$$
\begin{pmatrix}
1 & 0 \\
0 & 1
\end{pmatrix}
$$

$$\left(\begin{array}{cc}1& 0\\ 0& 1\end{array}\right)$$

Formulas that are too wide

$$f(x)=a_0+a_{1}x+a_2{x}^2+a_3{x}^3+a_4{x}^4+a_5{x}^5+a_6{x}^6+a_7{x}^7+a_8{x}^8+a_9{x}^9$$

The same applies here: what is too wide scrolls inside itself instead of blowing up the column.