Key concept in geometry often referred to as the "Basic Proportionality Theorem" or "Thales' Theorem." This theorem states that if a line is drawn parallel to one side of a triangle and intersects the other two sides at two distinct points, then this line divides those sides proportionally.
To understand it better, imagine a triangle ABC, where line DE is parallel to side BC, intersecting sides AB and AC at points D and E, respectively. According to the theorem, the segments on these sides are proportional, meaning that the ratio of AD to DB is equal to the ratio of AE to EC.
