# Missing \right inserted

This error appears when you have written a ** \left** command, without a corresponding

**command. The**

`\right`

**and**

`\left`

**commands are used for dynamically resizing parenthesis. The delimiters allowed which can be used with**

`\right`

**and**

`\left`

**commands are**

`\right`

**or the dot**

`() [] | \| \{ \}`

**. If you do not use the**

`.`

**and**

`\left`

**commands when placing parentheses around large items such as fractions and integrals, the parenthesis will not be the same size as the expression contained:**

`\right`

You can place fitted brackets around a fraction by writing ** \left( \frac{x}{y} \right)**. This will create nicer looking parenthesis which are the same size as the expression contained within them:

If you write a ** \left** command, but do not finish the expression with a

**command, you will generate the error shown below:**

`\right`

main.tex, line 5

<inserted text> \right . l.5 \[ \left(x=\frac{1}{2} \] I've inserted something that you may have forgotten. (See the <inserted text> above.) With luck, this will get me unwedged. But if you really didn't forget anything, try typing `2' now; then my insertion and my current dilemma will both disappear. [1

# Common Causes

**Forgetting to include a \right:**

The most basic cause of this error occurs when you have written a ** \left** command but have forgotten to include a corresponding

**as shown below:**

`\right`

\[ \pi = \left( \int_{-\infty}^{+\infty} e^{-x^2} dx ) \]

This will generate an error as we have written a ** \left** at the start of our expression, but we have not written a

**at the end of it. The correct way to write this expression is:**

`\right`

\[ \pi = \left( \int_{-\infty}^{+\infty} e^{-x^2} dx \right) \]

If you would like to only have a ** \left** delimiter, with no

**, you can solve this by including a**

`\right`

**. The dot indicates that this**

`\right.`

**will be blank.**

`\right`

**Using \left and \right commands around alignment characters:**

Another common mistake is when ** \left** and

**commands are used around alignment characters as shown below:**

`\right`

\begin{align} f(x) = \left( 1 &+ 2x \right)\\ + \left( 3x^2 &+ 4x^3 \right) \end{align}

This is not allowed, and will cause an error to be generated. The correct way to write this is to use ** \bigl** and

**commands as shown below:**

`\bigr`

\begin{align} f(x) = \bigl( 1 &+ 2x \bigr)\\ + \Bigl( 3x^2 &+ 4x^3 \Bigr) \end{align}

These ** \bigl** and

**commands are not dynamically fitted, and are a set size. The size will need to be chosen by hand, however they pose the advantage of not needing to be paired in the same way as**

`\bigr`

**and**

`\left`

**commands. The choices of sizing -- in order of increasing size -- are**

`\right`

**,**

`\big`

**,**

`\Big`

**, and**

`\bigg`

**. If you use these statements in pairs, such as**

`\Bigg`

**and**

`\biggl[`

**, LaTeX will perform some syntax checking for you.**

`\biggr]`

**Using \left for piecewise functions:**

A common cause of error occurs when writing piecewise functions such as the one shown below:

If you write this as:

\[ f(x)= \left\{ \begin{array}{lr} 0 & x\leq 0 \\ 1 & x > 0 \end{array} /]

you will generate an error, as there is no ** \right**. One way around this would be to include a blank

**by writing**

`\right`

**as shown below:**

`\right.`

\[ f(x)= \left\{ \begin{array}{lr} 0 & x\leq 0 \\ 1 & x > 0 \end{array} \right. /]

A better way to write this is to avoid ** \left** and

**commands entirely by using the**

`\right`

**enviromnent provided by the**

`cases`

**environment as shown below:**

`amsmath`

% In your preamble \usepackage{amsmath} % In the main body of your document \[ f(x)= \begin{cases} 0 & x\leq 0 \\ 1 & x > 0 \end{cases} /]

**Using line breaks inside \left and \right commands:**

When writing long expressions, you sometimes may want to include line breaks as shown below:

The number of ways of writing a number $n$ as a sum of positive integers is given by \begin{align*} p(n)= &\frac{1}{\pi \sqrt{2}} \sum_{k=1}^\infty \sqrt{k} A_k(n) \frac{d}{dn} \left({\frac {1} {\sqrt{n-\frac{1}{24}}} \\ &\times \sinh \left[ {\frac{\pi}{k} \sqrt{\frac{2}{3}\left(n-\frac{1}{24}\right)}}\right] }\right) \end{align*}

This will generate an error, as we are not allowed to include a line break ** \\** inside

**and**

`\left`

**commands. The correct way to write this expression is to once again use**

`\right`

**and**

`\Biggl`

**commands as shown below:**

`\Biggr`

The number of ways of writing a number $n$ as a sum of positive integers is given by \begin{align*} p(n)= &\frac{1}{\pi \sqrt{2}} \sum_{k=1}^\infty \sqrt{k} A_k(n) \frac{d}{dn} \Biggl({\frac {1} {\sqrt{n-\frac{1}{24}}} \\ &\times \sinh \Biggl[ {\frac{\pi}{k} \sqrt{\frac{2}{3}\Biggl(n-\frac{1}{24}\Biggr)}}\Biggr] }\Biggr) \end{align*}

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