One of the components of “Display Math mode” is number equations. There are many methods in LaTeX for this. Each method is discussed in depth with code and output below.

## Use equation environment for single line equation

Our first method is equation-environment, which will return you a single line number equation. This environment does not support multi-line number equations. But, there is an optional method for this.

```
\documentclass{article}
\usepackage{lipsum}
\begin{document}
\lipsum[1][1-4]
\begin{equation}
f(x)= \int \frac{\ln x}{x} {dx} = \frac{\left(\ln x\right)^2}{2}
\end{equation}
\lipsum[2][1-3]
\begin{equation}
\int \tan^2(x){dx} = \frac{1}{n-1}\tan^{n-1}(x)-\int \tan^{n-2}(x){dx}
\end{equation}
\lipsum[3][1-3]
\begin{equation}
\int x^n {dx} = \frac{x^{n+1}}{n+1} + C, n \neq -1
\end{equation}
\end{document}
```

**Output :**

## Equation with split environment for multi-line

For multi line, `split`

Environment is used with Equation. In LaTeX, this environment does not have a default. So, `amsmath`

package must be called within preamble.

It will be easier, if you understand the structure of syntax. `&`

symbol shift one equation left-aligned relative to another, so that each equation’s left margin or left indent is equal with respect to the page.

And `\\`

symbols will break the line. If there are `n`

equations then `\\`

symbols will be used `n-1`

times.

```
\documentclass{article}
\usepackage{lipsum,amsmath}
\begin{document}
\lipsum[1][1-4]
\begin{equation}
\begin{split}
f(x)&=\int\frac{\ln x}{x} {dx} \\
&= \int \ln x \; {d(\ln x)} \\
&= \frac{\left(\ln x\right)^2}{2} +C
\end{split}
\end{equation}
\lipsum[2][1-3]
\begin{equation}
\begin{split}
&\frac{d}{dx} (\sin x) = \cos x \\
&\frac{d}{dx} (\cos x) = -\sin x \\
&\frac{d}{dx} (\tan x) = -\sec^2 x
\end{split}
\end{equation}
\lipsum[3][1-3]
\begin{equation}
\begin{split}
\sum_{i=1}^n i = \frac{n(n+1)}{2}
\end{split}
\end{equation}
\end{document}
```

**Output :**

Interestingly, this nested environment will return a number for the entire system of equations or multi line equations. If you want only one number for the whole system, then you can take help of `split`

environment.

## Use align environment

`align`

environment will return a separate equation number for each equation. Its structure will be composed of `&`

and `\\`

symbols that we saw in the above point of use.

```
\documentclass{article}
\usepackage{lipsum,amsmath}
\begin{document}
\lipsum[1][1-4]
\begin{align}
&\frac{d}{dx} (\sin x) = \cos x \\
&\frac{d}{dx} (\cos x) = -\sin x \\
&\frac{d}{dx} (\tan x) = -\sec^2 x
\end{align}
\lipsum[2][1-3]
\begin{align}
f(x)&=\int\frac{\ln x}{x} {dx} \\
&= \int \ln x \; {d(\ln x)} \\
&= \frac{\left(\ln x\right)^2}{2} +C
\end{align}
\lipsum[3][1-3]
\begin{align}
\sum_{i=1}^n i = \frac{n(n+1)}{2}
\end{align}
\end{document}
```

**Output :**

## Use flalign environment

Using `flalign`

environment is similar to `align`

environment. And with this environment you can shift the equation completely to left. That is advantage of this environment

```
\documentclass{article}
\usepackage{lipsum,amsmath}
\begin{document}
\lipsum[1][1-4]
\begin{flalign}
\frac{d}{dx} (\sin x) = \cos x \\
\frac{d}{dx} (\cos x) = -\sin x \\
\frac{d}{dx} (\tan x) = -\sec^2 x
\end{flalign}
\lipsum[2][1-3]
\begin{flalign}
f(x)&=\int\frac{\ln x}{x} {dx} \\
&= \int \ln x \; {d(\ln x)} \\
&= \frac{\left(\ln x\right)^2}{2} +C
\end{flalign}
\lipsum[3][1-3]
\begin{flalign}
\sum_{i=1}^n i = \frac{n(n+1)}{2}
\end{flalign}
\end{document}
```

**Output :**

## Use gather environment

The `gather`

environment will return multi line, **but not support alignment**. In this case, `\\`

is used for multi-line.

```
\documentclass{article}
\usepackage{lipsum,amsmath}
\begin{document}
\lipsum[1][1-4]
\begin{gather}
\frac{d}{dx} (\sin x) = \cos x \\
\frac{d}{dx} (\cos x) = -\sin x \\
\frac{d}{dx} (\tan x) = -\sec^2 x
\end{gather}
\lipsum[2][1-3]
\begin{gather}
f(x)=\int\frac{\ln x}{x} {dx} \\
= \int \ln x \; {d(\ln x)} \\
= \frac{\left(\ln x\right)^2}{2} +C
\end{gather}
\lipsum[3][1-3]
\begin{gather}
\sum_{i=1}^n i = \frac{n(n+1)}{2}
\end{gather}
\end{document}
```

**Output :**