Three points A, B and C lie on one straight line. AB = 15cm, BC = 18cm, find the distance AC.

By condition, the segments AB and BC have a common point. All points are on one straight line. The relative position of the segments can have two options: in the first case, from point B, the segments AB and BC diverge in different directions, in the second case, in one direction.

Then, in the first case, the length of the segment AC = AB + BC = 15 + 18 = 23 cm.

In the second case, the length of the segment AC = BC – AB = 18 – 15 = 3 cm.

Answer: The length of the AC segment can be 23 cm or 3 cm.