Math Homework. Do It Faster, Learn It Better.

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 A C ¯ , then A B + B C = A C .

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 X Y in the figure shown.

By the Segment Addition Postulate, X Y + Y Z = X Z .

Substitute the given values.

X Y + 11 = 17

Solve for X Y .

X Y = 6