#### Transcript Points, Lines, and Planes - Onondaga Central School District

```Refresher…
• ABC is isosceles
• Line CD bisects C and is
a perpendicular bisector to
AB
• If mA is 50, find mB,
mACD, and mACB
• *After notes are done, you
will be allowed to do quiz
corrections in class.*
Midsegments of Triangles
Geometry
Mrs. King and Mr. Zampetti
Unit 4, Day 4
Definition
• Midpoint – The point that divides the
segment into two congruent segments.
A
M
B
Definition
• Midsegment of a Triangle – a segment
connecting the midpoints of two of its
sides.
B
M
A
N
C
Draw a Midsegment:
• In your notes, draw ABC.
• Find the midpoint of AC and call it point
M.
• Find the Midpoint of BC and call it point
N.
• Measure MN and AB. What do you
notice?
Midsegment
•
M is a midpoint of AB
•
N is a midpoint of BC
•
MN is a midsegment of ABC
M
A
B
N
C
Triangle Midsegment Theorem
• If a segment joins the midpoints of a
triangle, then the segment is parallel to the
third side of the triangle and half its length
How it is used:
• Find x:
B
x
M
A
16
N
C
How it is used:
•
•
•
•
LM is a midsegment of ABC
If AL = 4, what does AB = ?
If LM = 5, what does AC = ? B
If BC = 18, what does CM = ?
• AB = 8
• AC = 10
• CM = 9
L
A
M
C
Practice
• In quadrilateral EFGH, the points A, B, C, and D
are midpoints and EG = 18 cm. Find AB and
CD.