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 AC ¯ , then AB+BC=AC .

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

Example:

Find the length XY in the figure shown.

By the Segment Addition Postulate, XY+YZ=XZ .

Substitute the given values.

XY+11=17

Solve for XY .

XY=6