\documentclass[12pt]{jsarticle}
\usepackage{amsmath,amssymb}
\pagestyle{empty}
\begin{document}
\setlength{\baselineskip}{22pt}
\begin{flushleft}
{\huge 3}
　数列$\{ \theta_k \}$が$\displaystyle\cos\theta_k=1-\frac{1}{2k^2}$を満たすとき，
$\displaystyle\sum_{k=1}^n\tan^2\frac{\theta_k}{2}$を求めよ．
\end{flushleft}
\end{document}
