The Segment Addition Postulate

The phrase "Segment Addition Postulate" can be a little intimidating, especially at the beginning of a Geometry or Honors Geometry course.

We'll show you that this postulate is nothing more than breaking sticks...and then putting them back together.

Activity

Go find a stick in your back yard - or use a skewer like the one shown here (be careful of the sharp end). Licorice is a safe alternative. 

Measure the length of your object.  Our skewer is 8 inches long.

Break the object into 2 pieces and  measure the length of both pieces.  Our pieces are 2 inches, and 6 inches long.

Finally, put the two pieces back together.  Measure the length of the skewer or stick now that it is put back together.

Our skewer is still 8 inches like it was originally.  Does this seem easy and obvious?  Good, it should!

Congratulations, you just modeled the postulate.

Formal Definition

The Postulate says that if point Q is between points P and R on a line, then PQ + QR = PR. Look at the diagram below.

All this means is...if you take one piece of a segment (PQ), and add it to another piece of a segment (QR), you get the entire segment (PR).  "The sum of the parts equals the whole."

Return from Segment Addition Postulate to Free Geometry Help.