I haven't opened it even once. This is a revised edition of Mathematics I・A, featuring easy-to-understand explanations with a problem set. - Title: Easy High School Mathematics - Author: Hiroshi Sadaoka - Edition: Revised Edition - Subject: Mathematics I・A - Publisher: Gakken - Features: Includes problem set, easy-to-understand explanations - Contents: Contains 70 problems - Language: Japanese Thank you for looking.