1. Classifying Triangles & Angles of Triangles
Sections 4-1 & 4-2

2. A triangle is the figure formed by 3 segments joining 3 noncollinear points. Each of the 3 points is a vertex. The segments are the sides. A C B

3. Classifying Triangles by Sides
Scalene Triangle –
no sides congruent
Isosceles Triangle –
At least 2 sides congruent
Equilateral Triangle –
All sides congruent

4. Classifying Triangles by Angles
700
Acute – 3 acute angles
500
600
Right – 1 right angle
400
Obtuse – one obtuse angle
200
1200
600
Equiangular – all angles congruent
600
600

5. Parts of an Isosceles Triangle
vertex angle
leg
leg
base
base angles

6. The sum of the measures of the angles of a triangle is 180.
Angle Sum Theorem
The sum of the measures of the angles of a triangle is 180.
1000
400
400

7. Third Angle Theorem
If 2 angles of one triangle are congruent to 2 angles of another triangle, then the third angles are congruent.

8. Corollaries statements that can be easily proved using a theorem
Each angle of an equiangular triangle has measure 60.
In a triangle, there an be at most one right angle or obtuse angle.
The acute angles of a right triangle are complementary.

9. Exterior Angle Theorem
The measure of an exterior angle of a triangle equals the sum of the measures of the 2 remote interior angles.
Remote interior
angles
350
Exterior
750
400

10. Joke Time
What has wings and solves number problems?
A mothematician

11. What did one math book say to the other math book?
Don’t bother me! I’ve got my own problems!

12. What would a math student say to a fat parrot?
Poly-no-mial