\documentclass[12pt]{jsarticle}
\usepackage{amsmath,amssymb}
\pagestyle{empty}
\begin{document}
\setlength{\baselineskip}{22pt}
\begin{flushleft}
{\huge 4}
　$-1<a<1$とする．
\begin{description}
\item[(1)]積分$\displaystyle\int_0^a\frac{1}{1-x^2}dx$を求めよ．
\item[(2)]$n=1,2,3,\cdots$のとき，つぎの等式を示せ．
\[ \int_0^a\frac{x^{2n+2}}{1-x^2}dx=
\frac{1}{2}\log\frac{1+a}{1-a}-\sum_{k=0}^n\frac{a^{2k+1}}{2k+1} \]
\item[(3)]つぎの等式を示せ．
\[ \log\frac{1+a}{1-a}=2\sum_{k=0}^\infty\frac{a^{2k+1}}{2k+1} \]
\end{description}
\end{flushleft}
\end{document}
