This document is a chapter from a Greek first year high school mathematics textbook. It covers the topics of positive and negative real numbers, absolute value, opposites, and comparing real numbers. Some key points covered include: defining positive and negative numbers, their placement on the number line; absolute value as the distance from zero; opposites having the same absolute value but different signs; and the absolute value of positive numbers being themselves and negatives being their opposites. Examples are provided to illustrate these concepts along with exercises for students to practice.