1. Triangles and Lines – Introduction to Triangles
Triangle - a closed plane with three sides
- the points that create the sides are vertices
vertices

2. Triangles and Lines – Introduction to Triangles
Triangle - a closed plane with three sides
- the points that create the sides are vertices
- labeled using CAP letters in sequence and symbol is ∆ A
∆ABC
vertices C B

3. Triangles and Lines – Introduction to Triangles
Triangle - a closed plane with three sides
- the points that create the sides are vertices
- labeled using CAP letters in sequence and symbol is ∆
- angles are formed a t the vertices and their sum = 180° A
∆ABC contains
angles C B

4. Triangles and Lines – Introduction to Triangles
Triangle - a closed plane with three sides
- the points that create the sides are vertices
- labeled using CAP letters in sequence and symbol is ∆
- angles are formed a t the vertices and their sum = 180° A
sides C B a
- sides are also labeled using small letters and named as their opposite angle partner

5. Triangles and Lines – Introduction to Triangles
Triangle - a closed plane with three sides
- the points that create the sides are vertices
- labeled using CAP letters in sequence and symbol is ∆
- angles are formed a t the vertices and their sum = 180° A b
sides C B a
- sides are also labeled using small letters and named as their opposite angle partner

6. Triangles and Lines – Introduction to Triangles
Triangle - a closed plane with three sides
- the points that create the sides are vertices
- labeled using CAP letters in sequence and symbol is ∆
- angles are formed a t the vertices and their sum = 180° A b c
sides C B a
- sides are also labeled using small letters and named as their opposite angle partner

7. Triangles and Lines – Introduction to Triangles
Triangle - a closed plane with three sides
- the points that create the sides are vertices
- labeled using CAP letters in sequence and symbol is ∆
- angles are formed a t the vertices and their sum = 180° A
sides C B
- sides are also labeled using small letters and named as their opposite angle partner OR as segments

8. Triangles and Lines – Introduction to Triangles
Types of triangles
Equilateral – 3 equal sides and angles ( all angles = 60°)
Isosceles – two equal sides and angles
60°
60°
60°

9. Triangles and Lines – Introduction to Triangles
Types of triangles
Equilateral – 3 equal sides and angles ( all angles = 60°)
Isosceles – two equal sides and angles
60°
60°
60°
Use marks like this to show sides are equal

10. Triangles and Lines – Introduction to Triangles
Types of triangles
Equilateral – 3 equal sides and angles ( all angles = 60°)
Isosceles – two equal sides and angles
60°
60°
60°
The two equal sides are called legs
leg
leg

11. Triangles and Lines – Introduction to Triangles
Types of triangles
Equilateral – 3 equal sides and angles ( all angles = 60°)
Isosceles – two equal sides and angles
60°
60°
60°
The two equal sides are called legs
leg
leg
The third side is called the base
base

12. Triangles and Lines – Introduction to Triangles
Types of triangles
Equilateral – 3 equal sides and angles ( all angles = 60°)
Isosceles – two equal sides and angles
60°
60°
60°
The two equal sides are called legs
leg
leg
The third side is called the base
base
The two equal angles are called base angles

13. Triangles and Lines – Introduction to Triangles
Types of triangles
Equilateral – 3 equal sides and angles ( all angles = 60°)
Isosceles – two equal sides and angles
60°
60°
60°
The third angles is called the vertex angle
The two equal sides are called legs
leg
leg
The third side is called the base
base
The two equal angles are called base angles

14. Triangles and Lines – Introduction to Triangles
Types of triangles
Scalene – no equal sides or angles
Obtuse – contains an angle greater than 90°
Right - has a 90° angle