Segments and midpoints
Find segment lengths using the segment addition postulate and locate midpoints.
Objective
Find segment lengths using the segment addition postulate and locate midpoints.
What it means
The midpoint of a segment is the point that divides it into two congruent halves. The segment addition postulate says that if B is between A and C, then AB + BC = AC.
Key terms
- Segment
- A part of a line with two endpoints.
- Midpoint
- The point exactly halfway between two endpoints of a segment.
- Bisect
- To divide into two equal parts.
- Segment addition postulate
- If B is between A and C, then AB + BC = AC.
Rules to remember
- If M is the midpoint of AB, then AM = MB = (1/2)AB.
- If B is between A and C, AB + BC = AC.
Step by step
- 1Draw or picture the segmentMark the endpoints and any given point on it.
- 2Apply the right ruleUse segment addition for a between-point, or the midpoint formula for equal halves.
- 3Solve for the unknownSet up and solve the resulting equation.
Common mistakes
- Forgetting the midpoint splits a segment into two EQUAL parts, not just any two parts.
- Adding lengths when a point is not actually between the other two.
Tips
- Sketch a quick number-line picture of the segment before writing equations.