# Typesetting one-step equations

The letters l and r stand for left-alignment and right-alignment respectively. Notice the columns are aligned rrlr. There are six columns because align and alignat are comprised of lr pairs, because alignment often involves hugging both sides of =. Whenever we are adding or subtracting from both sides, we want right alignment. The alignment of = doesn't matter. In this case, it was simpler to use l, but we could have used r for the same effect. Unfortunately, we can't use MathJax, because it doesn't support `\cline`

, and every workaround makes the code god-awful.

```
\documentclass[margin=10pt]{standalone}
\begin{document}
$\arraycolsep=0pt
\begin{array}{rrcr}
x & {} + 3 & {} = {} & 7 \\
& {} - 3 & & {} - 3 \\
\cline{2-2}\cline{4-4}
x & & = & 4
\end{array}$
\end{document}
```

Division problems are a bit different, because of the fraction bar. My preferred style mimics how I would solve such an equation on paper. Here it is:

```
$$\begin{align}
\dfrac{x}{3} &= 24 \\[1em]
3 \cdot \dfrac{x}{3} &= 24 \cdot 3 \\[1em]
x &= 72
\end{align}$$
```

$$\begin{align}
\dfrac{x}{3} &= 24 \\[1em]
3 \cdot \dfrac{x}{3} &= 24 \cdot 3 \\[1em]
x &= 72
\end{align}$$
Also, important to note, if you want space to appear on both sides of the operator, yet only the second operand is present, you do `{} + 3`

. If you want space on just one side of the operator, say, the right, do `+\>3`

. I haven't found a reason to ever type this, but it might be useful later!