1. Triangles and Angles

2. Classifying Triangles
Line segments are congruent if they have the same length
One way to classify triangles is by the number of congruent sides they have

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 angle by it’s sides and it’s angles:
Angle: Angle: Angle:
Side: Side: Side:
Acute
Equilateral
Obtuse
Scalene
Right
Isosceles

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

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

8. 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.

9. 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
180 degrees

10. Triangle Mini-Lab
Flip over one angle and use your protractor to measure it.
Write the measure on the back of the angle and repeat these steps for the other two angles.
Add up the measures of each of the angles.

11. Finding The Measures of Angles
In an equilateral triangle, all of the sides are congruent and all of the angle measurements are congruent
What is the measure of each angle?

12. Finding The Measures of Angles
What do we know?
We know that each angle is congruent but we don’t know their measure. Let’s call it “X.”
We know that all three angles add up to 180 degrees. Therefore, X + X + X = 180
What is the measure of each angle?
3x = 180
X = 60

13. Finding The Measures of Angles Checkpoint
Find the measure of each triangle then
classify the triangle by it’s angles:
m a = 46,
m b = 42,
m c =
Classify:
x = 180
x + 88 = 180
x = 92
Obtuse

14. Finding The Measures of Angles Checkpoint
Find the measure of each triangle then
classify the triangle by it’s angles:
m a = 3x,
m b = 2x,
m c = x
Classify:
3 x 30 = 90
2 x 30 = 60
x = 30
x + 2x + 3x = 180
6x = 180
x = 30
Right

15. Finding The Measures of Angles Checkpoint
Find the measure of each triangle then
classify the triangle by it’s angles:
m a = 4x,
m b = 3x,
m c = 2x
Classify:
4 x 20 = 80
3 x 20 = 60
2 x 20 = 40
4x + 3x + 2x = 180
9x = 180
x = 20
Acute

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