Aligning equations

Lining equations up

When you show working, readers like the = signs to line up. The align* environment does this:

\begin{align*}
  y &= 2(x + 3) \\
  y &= 2x + 6
\end{align*}

The & marks where to align (just before each =), and \\ ends each line.

$The align environment lines the equals signs up at each ampersand$

Numbered or not

align* (with the star) gives no equation numbers.
Drop the star — align — and LaTeX numbers each line (1), (2), … for you to refer to.

Matrices

amsmath also gives matrices. bmatrix draws square brackets:

\[
  \begin{bmatrix} 1 & 2 \\ 3 & 4 \end{bmatrix}
\]

Again & separates columns and \\ separates rows — the same idea as alignment.

Common mistakes

In align, line up on & and end each line with \\.
Use align* when you do not want equation numbers.

Show the two steps lined up at the = sign. Put them in an align* environment, with & just before each = and \\ between the lines.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[ y = 2(x + 3) \]
\[ y = 2x + 6 \]
\end{document}

Click Run to compile and preview the PDF.

Draw a 2×2 matrix with bmatrix (square brackets). Separate columns with & and rows with \\, e.g. \begin{bmatrix} 1 & 2 \\ 3 & 4 \end{bmatrix}.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
  % write a 2x2 bmatrix here
\]
\end{document}