\begin{frame}
\frametitle{The Definite Integral}
\begin{exampleblock}{}
The integral is a number.
\medskip
The variable name $x$ does not influence the integral:
\begin{talign}
\int_{a}^{b} f(x)dx = \int_{a}^{b} f(t)dt = \int_{a}^{b} f(r)dr
\end{talign}
\end{exampleblock}
\end{frame}