In the given triangle, find the
value of x, and the m<ABC.

In the figure shown below, segment BD bisects
segment AC, and segment AB is congruent to
segment BC.
 Prove that triangle ADB and triangle CDB
are right triangles. Use a two-column
proof.

 The area of the triangle is
equal to the area of the
parallelogram.
What can you
conclude about the
area of the two
shapes?
Area of triangle Area = ½ (B x H)
Area of
parallelogram
Area = B x H

The segment joining the midpoints of two
sides of a triangle is parallel to the third
side and is half as long as the third side.
Midline
Theorem

Example 1:
Find the
value of x.

B is the midpoint of segment AC, D is the
midpoint of segment CE, and AE = 17.
Find BD.
Example 2:

a. If AC = 10 and AB = 16, find
AD, BE, and DE.
b. If AC = x - 10 and DE = 6, find
the value of x.
ABC is an
isosceles
triangle
with base
AC and
midline DE.

Find the
value of x,
y, and z.

x = ___ AB = ___
y = ___ AC = ____
z = ___ CB = ____
m ABC = _____ m DEB = _________
m ADE = _______m EDC = _________
m ACB = _______
D is the midpoint of segment AC, E is the
midpoint of segment AB.

Write Summary
 At least 3 sentences

1. ABC is an isosceles triangle with
base and midline
If AC = 10 and AB = 16, find:
AD = _______ BE = ______
DE = _______
2. If AC = x – 10 and DE = 6, find the
value of x.
E
D
A
B
C