1. Section 4-1
Triangles and Angles

2. triangle
A figure formed by three segments jining three noncollinear points.

3. Triangles are classified by their sides and angles.

4. Side Classification: Equilateral Triangle: 3 congruent sides
Isosceles Triangle: at least 2 congruent sides
Scalene Triangle: No congruent sides

5. Isosceles Triangle
Equilateral Triangle
Scalene Triangle

6. Angle Classification:
Acute Triangle: 3 acute angles
Equiangular Triangle: 3 congruent angles
Right Triangle: 1 right angle
Obtuse Triangle: 1 obtuse angle

7. Acute Triangle
Right Triangle
Obtuse Triangle
Equiangular Triangle

8. When naming a triangle you must be as specific as possible!
Name triangles by BOTH sides and angles!

9. Some Examples: 1.
Equilateral Equiangular 2.
Obtuse Isosceles

10. Parts of a triangle: The segments are called the sides of a triangle
Each of the three points is a vertex of the triangle
Two sides sharing a common vertex are adjacent sides

11. B A C
Sides:
Vertices: A, B, C

12. Parts of a right triangle:
Leg: the sides that form the right angle
Hypotenuse: the side opposite the right angle (longest side)

13. Hypotenuse
Leg
Leg

14. Parts of an isosceles triangle:
When it has only two congruent sides:
Leg: two congruent sides
Base: the 3rd side

15. Leg
Leg
Base