数学のたまご<BODY bgcolor=#e0ffff text=#2f4f4f link=#32cd32 vlink=#00ff00 alink=#00fa9a> <A name="_pageHead"></A> <TABLE align="center" border="0" width="640" cellpadding="0" cellspacing="0"> <TBODY> <TR align="left" valign="top"> <TD align="left" valign="top" width="640" nowrap> <TABLE border="0" width="200" height="235" cellpadding="0" cellspacing="0"> <TBODY> <TR align="left" valign="top"> <TD align="cente
平行四辺形の定義
