LaTeX error · Math mode

Missing \right. inserted.

The error in the log

This is how the message appears in the .log file (and in the compile output). The line starting with l. is the line number where TeX noticed the problem; the real mistake is there or just before it.

! Missing \right. inserted.
<inserted text> 
                \right .
l.5 The ratio is $f(x) = \left( \frac{a}{b}$
                                            .

Why it happens

• A \left( whose \right) was forgotten or deleted.
• A \left ... \right pair split across & or \\ in align, split or an array. Each cell and each line is its own group; inside align the same mistake is reported as Extra }, or forgotten \right.
• The pair split across braces, for example {\left( x} \right), so the two halves are in different groups.

How to fix it

Add the \right) before the formula ends. In a multi-line equation, close the delimiter in the same line and cell. When a bracket has to span two lines, end the first line with an invisible \right. and start the second with \left., or use manual sizes (\Bigl( ... \Bigr)), which work across lines because they are not paired.

Broken: reproduces the error

\documentclass{article}

\begin{document}

The ratio is $f(x) = \left( \frac{a}{b}$.

\end{document}

Fixed: compiles cleanly

\documentclass{article}

\begin{document}

The ratio is $f(x) = \left( \frac{a}{b} \right)$.

\end{document}

Extra \right.

! Extra \right.
l.5 Text $ (a+b) \right)
                         $

The mirror image: a \right with no matching \left before it in the same group. It usually happens when the \left was deleted, or when it sits on the previous line of an align or inside a different pair of braces.

Add the missing \left, or drop the \right and write the plain delimiter. In multi-line formulas use \left. at the start of the line to give the \right a partner.

Related errors

• Missing $ inserted – A math-only symbol (_, ^, \alpha) was used in text, or math mode was left early.
• \begin{split} won't work here – split used outside a math display; wrap it in equation (or use align).
• Extra alignment tab – A table row has more & separators than the column specification allows.
• All LaTeX errors and warnings – The full list, grouped by cause

Frequently Asked Questions

What does \right. mean?

\right. is an invisible closing delimiter. It satisfies the pairing rule without printing anything, which is how you close a \left on one line of a multi-line equation.

Can \left and \right span several lines of align?

No. Each line, and each cell between & signs, is typeset separately, so the pair must be complete on one line. Use \left( ... \right. on the first line and \left. ... \right) on the next, or fixed sizes like \Bigl( and \Bigr).

What causes Extra \right?

A \right that has no \left in the same group. Check for a deleted \left, or a pair split across &, \\ or braces.