答案1
\documentclass{beamer}
\linespread{1.5}\selectfont % <---
%\renewcommand\baselinestretch{1.5}\selectfont % <--- alternatively
\begin{document}
\begin{frame}
line 1
line 2
\end{frame}
\end{document}
\documentclass{beamer}
\linespread{1.5}\selectfont % <---
%\renewcommand\baselinestretch{1.5}\selectfont % <--- alternatively
\begin{document}
\begin{frame}
line 1
line 2
\end{frame}
\end{document}