1. Warm-up 1. How many degrees are in a triangle?
2. Classify the different types of triangles
By Angle Measures By Side Lengths

2. Triangle Sum Theorem:
The sum of the measures of the angles of a triangle is 180°.
m<DA + m<DB + m<DC = 180°. A C B

3. Classifying Triangles
By Angle Measures
Equiangular
Acute
Right
Obtuse
By Side Lengths
Equilateral
Isosceles
Scalene

4. Example 1:
Ex. 1 Find the m < Z
m < Z = 65

5. Example 2: Ex. 2 In triangle ABC, <ACB is a right angle, and
CD AB. Find the values of a, b, and c.
a = 70°
b = 20°
c = 20°

6. Example 3: Classify the triangles by their angles and sides
Right Isosceles
Obtuse Scalene

7. Corresponding Parts
The matching parts of two figures.

8. Congruent Triangles
Triangles (actually ALL geometric figures) that are the same ___________ and ___________ are ___________.
Each triangle has ______ sides and ________ angles.
If all _____ of the _______________ parts are ___________ then the triangles are ___________.

9. Midsegment
A midsegment of a triangle is a segment that connects the midpoints of 2 sides of the triangle. Every triangle has 3 midsegments.

10. Midsegment Theorem
The segment connecting the midpoints of 2 sides of a triangle is parallel to the third side and is half as long as that side
DE = ½ AC

11. Find the value of x
x = 3
x = 4

12. KH = 14
GK = 22
ST = 40

13. Give it a try…
X is the midpoint of MN, Y is the midpoint of NO, and Z is the midpoint of MO.
a. Find XZ.
XZ = 9
b. If XY = 10, find MO.
MO = 20

14. In triangle ACE, B is the midpoint of
AC and D is the midpoint of CE.
Find the value of x if
a. AB = 4x – 5 and AC = 3x + 15
b. CD = 6x – 4 and DE = 4x + 8