unknown error in table [closed]

Question

In the code for a table below, there is an error indicated by the red marker in the line starting with "Not protest" after compilation, although the output seems pretty much okay. Can you pinpoint the mistake please?

\documentclass{article}
%\usepackage{showframe}% http://ctan.org/pkg/showframe
\usepackage{booktabs}% http://ctan.org/pkg/booktabs
\usepackage{array}% http://ctan.org/pkg/array
\usepackage{tabularx}% http://ctan.org/pkg/tabularx
\usepackage{booktabs}% http://ctan.org/pkg/booktabs
\usepackage{array}% http://ctan.org/pkg/array
\usepackage{tabularx}% http://ctan.org/pkg/tabularx
\usepackage{calc}
\usepackage{tabu}
\begin{document}

\begin{table}[h]

\centering

\begin{tabular}{|c|c|c|}

\hline
 & $N^{e}$ \textless $K_i$ & $N^{e} \geq T_i$\\
\hline
 Not protest & $ -\Delta U $ & $(1-\gamma) \cdot \Delta U}$ \\
\hline
Protest & $-(k/N^{e})-\Delta$ U& $\Delta U - (k/N^{e})$\\
\hline

\end{tabular}

\caption{Payoff matrix}

\end{table}

\end{document}

Answer 1

You have a bracket too much after the \Delta in the line you mentioned (the one starting with 'Not protest'.

\begin{table}[h]
\centering

\begin{tabular}{|c|c|c|}

\hline
 & $N^{e} < K_i$ & $N^e \geq T_i$\\
\hline
 Not protest & $ -\Delta U $ & $(1-\gamma) \cdot \Delta U$ \\
\hline
Protest & $-(k/N^{e})-\Delta U$ & $\Delta U - (k/N^e)$\\
\hline

\end{tabular}
\caption{Payoff matrix}
\end{table}

Answer 2

an error?

TeX says

! Extra }, or forgotten $.
l.22 ... -\Delta U $ & $(1-\gamma) \cdot \Delta U}
                                                  $ \\
? h
I've deleted a group-closing symbol because it seems to be
spurious, as in `$x}$'. But perhaps the } is legitimate and
you forgot something else, as in `\hbox{$x}'. In such cases
the way to recover is to insert both the forgotten and the
deleted material, e.g., by typing `I$}'.

How much clearer do you want TeX to be? Learn to read the log file, please.