# I need to solve the problem of Missing delimiter (. inserted)?

{\small
\begin{multline}
\label{eq:kinem}
^{i-1}\mathit{T}_i = \left[
\begin{matrix}
\cos^2\phi_i(\cos\kappa_i s_i -1)+1 \\
\sin\phi_i \cos\phi_i (\cos\kappa_i s_i -1) \\
\cos\phi_i \sin\kappa_i s_i\\
0 \\
\end{matrix}\right.
\\
\left
\begin{matrix}
\sin\phi_i \cos\phi_i (\cos\kappa_i s_i -1)&-\cos\phi_i \sin\kappa_i s_i\\
\cos^{2}\phi_i (1-\cos\kappa_i s_i)+\cos\kappa_i s_i& -\sin\phi_i \sin\kappa_i s_i\\
\sin\phi_i \sin\kappa_i s_i&\cos\kappa_i s_i\\
0 & 0\\
\end{matrix}\right.
\\
\left.
\begin{matrix}
\dfrac{\cos\phi_i(\cos\kappa_i s_i -1)}{\kappa_i}\\
\dfrac{\sin\phi_i(\cos\kappa_i s_i -1)}{\kappa_i}\\
\dfrac{\sin\kappa_i s_i}{\kappa_i}\\
1
\end{matrix}\right]
\end{multline}}


After running this equation on Overleaf I got the following equation but the error still appeared Missing delimiter (. inserted) • Welcome to TeX.SX! Can you please expand the code snippet that you have posted to a full minimal working example. A MWE should compile and be as small as possible to demonstrate your problem. it's much easier to help you if we have full working code to start from. – Andrew Sep 30 at 11:54
• in the line with the \left command (just this one command) you have forgotten the .. like left. ... It is just what the error says. But there is no need as far as I see for this \left and its \right. since they are both ignored. – koleygr Sep 30 at 11:57

If you don't want brackets, then no need to give \left. and \right. You have to match your bracket size for starting and ending, for this, I used \vphantom, and the codes are follows:

\documentclass{book}
\usepackage{mathtools}

\begin{document}

{\small
\begin{multline}
\label{eq:kinem}
^{i-1}\mathit{T}_i = \left[
\begin{matrix}
\cos^2\phi_i(\cos\kappa_i s_i -1)+1\vphantom{\dfrac{\cos\phi_i(\cos\kappa_i s_i -1)}{\kappa_i}} \\
\sin\phi_i \cos\phi_i (\cos\kappa_i s_i -1) \vphantom{\dfrac{\sin\phi_i(\cos\kappa_i s_i -1)}{\kappa_i}}\\
\cos\phi_i \sin\kappa_i s_i\vphantom{\dfrac{\sin\kappa_i
s_i}{\kappa_i}}\\
0 \\
\end{matrix}\right.
\\
\begin{matrix}
\sin\phi_i \cos\phi_i (\cos\kappa_i s_i -1)&-\cos\phi_i \sin\kappa_i s_i\\
\cos^{2}\phi_i (1-\cos\kappa_i s_i)+\cos\kappa_i s_i& -\sin\phi_i \sin\kappa_i s_i\\
\sin\phi_i \sin\kappa_i s_i&\cos\kappa_i s_i\\
0 & 0\\
\end{matrix}
\\
\left.
\begin{matrix}
\dfrac{\cos\phi_i(\cos\kappa_i s_i -1)}{\kappa_i}\\
\dfrac{\sin\phi_i(\cos\kappa_i s_i -1)}{\kappa_i}\\
\dfrac{\sin\kappa_i s_i}{\kappa_i}\\
1
\end{matrix}\right]
\end{multline}}

\end{document}


Output As said in my comment, you don't really need the \left. (that you forgot the ".") and the \right. in your middle row:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\pagestyle{empty}
{\small
\begin{multline}
\label{eq:kinem}
^{i-1}\mathit{T}_i = \left[
\begin{matrix}
\cos^2\phi_i(\cos\kappa_i s_i -1)+1 \\
\sin\phi_i \cos\phi_i (\cos\kappa_i s_i -1) \\
\cos\phi_i \sin\kappa_i s_i\\
0 \\
\end{matrix}\right.
\\
\begin{matrix}
\sin\phi_i \cos\phi_i (\cos\kappa_i s_i -1)&-\cos\phi_i \sin\kappa_i s_i\\
\cos^{2}\phi_i (1-\cos\kappa_i s_i)+\cos\kappa_i s_i& -\sin\phi_i \sin\kappa_i s_i\\
\sin\phi_i \sin\kappa_i s_i&\cos\kappa_i s_i\\
0 & 0\\
\end{matrix}
\\
\left.
\begin{matrix}
\dfrac{\cos\phi_i(\cos\kappa_i s_i -1)}{\kappa_i}\\
\dfrac{\sin\phi_i(\cos\kappa_i s_i -1)}{\kappa_i}\\
\dfrac{\sin\kappa_i s_i}{\kappa_i}\\
1
\end{matrix}\right]
\end{multline}}

\end{document}


Output: 