Segment Addition Postulate

The segment addition postulate is a fairly obvious-seeming postulate which states that:

If a point B lies on a line segment , then .

That is, the distance from one endpoint to the other is the sum of the distances from the middle point to either endpoint.


Find the length XY in the figure shown.

By the Segment Addition Postulate, .

Substitute the given values.

Solve for XY.