1. Triangles and Angles

2. Classifying Triangles
Line segments are congruent if they have the same length; shown by the number of marks on the line segment
One way to classify triangles is by the number of congruent sides they have
Congruent

3. Classifying Triangles
Scalene Triangles have no congruent sides
Isosceles Triangles have two congruent sides
Equilateral Triangles have three congruent sides

4. Classifying Triangles
Another way to classify triangles is by the measure of their angles
Acute Triangles have three acute angles
Obtuse Triangles have one obtuse angle
Right Triangles have one right angle

5. Classifying Triangles Checkpoint
Classify each triangle by its sides and it’s angles:
Angle: Angle: Angle:
Side: Side: Side:
Acute
Equilateral
Obtuse
Scalene
Right
Isosceles

6. Triangle Mini-Lab Materials Needed: Pencil
Ruler (share with a neighbor)
Scissors (share with a neighbor)

7. Triangle Mini-Lab
Using a ruler and pencil, draw any large triangle and cut it out with scissors.
Individually label each angle 1, 2, and 3.
Tear off (do NOT cut) a large section of each angle and arrange so each vertex is touching and each angle is adjacent to the next.

8. Triangle Mini-Lab
What type of angle did the three angles form when placed together?
What is the measure of this angle?
Let’s confirm….
A straight angle
180º

9. Interior Angles of a Triangle
The sum of the measures of the angles of a triangle is 180

10. Finding The Measures of Angles Checkpoint
Find the measure of each angle then
classify the triangle by its angles:
m a = 46º,
m b = 42º,
m c =
Classify:
xº + 46º + 42º = 180º
xº + 88º = 180º
x = 92º
92º
Obtuse

11. Finding The Measures of Angles Checkpoint
Find the measure of each angle then
classify the triangle by its angles:
m a = 3xº,
m b = 2xº,
m c = xº
Classify:
xº + 2xº + 3xº = 180º
6xº = 180º
x = 30º
3(30º) = 90º
2(30º) = 60º
x = 30º
Right

12. Finding The Measures of Angles Checkpoint
Find the measure of each angle then
classify the triangle by its angles:
m a = 4xº,
m b = 3xº,
m c = 2xº
Classify:
4xº + 3xº + 2xº = 180º
9xº = 180º
x = 20º
4(20º) = 80º
3(20º) = 60º
2(20º) = 40º
Acute

13. Finding The Measures of Angles Checkpoint
Find the measure of each angle a° b°
c °
65 °
70 °
bº + 70º + 65º = 180º
bº + 135º = 180º
b = 45º
c is alternate interior with 65°
c = 65°
a is alternate interior with 70°
a = 70°

14. Finding The Measures of Angles Checkpoint
Find the measure of each angle
a is alternate interior with °
a = 123°
bº + 123º + 35º = 180º
bº + 158º = 180º
b = 22º
123° a° b°
35° c°
c is alternate interior with 35°
c = 35°

15. Homework Skill 6: Triangles (both sides)
6-2 Practice Skills: Triangles and Angles (both sides)
Due Tomorrow!