1. Lesson 3-3: Triangles Vocab: Equiangular Acute triangle Right triangle Obtuse triangle Equilateral triangle Isosceles triangle Scalene triangle Exterior angle

2. Angle Sum Theorem The sum of the measures of a triangle is 180 0 A B C “The measure of angle A plus the measure of angle B plus the measure of angle C equals 180”

3. Classify by angles Type of triangle PropertyDrawing AcuteAll angles < 90 0 ObtuseOne angle > 90 0 RightOne angle = 90 0

4. Classify by sides Type of triangle PropertyDrawing ScaleneNo sides = Isosceles 2 or more sides are = Equilateral3 sides =

5. Hints & suggestions What are the other angles in a… –Obtuse triangle: –Right triangle: Classify using angles & sides –Draw a right, isosceles triangle (use markings!) May have to use the distance formula Acute and add to 90 Acute

6. Exterior Angle Theorem ► An exterior angle is formed by extending a side outside the triangle Exterior angle Theorem: The measure of an exterior angle is equal to the sum of its remote interior angles. Remote interior angles A B CX 1 2 3 4 And don’t forget…

7. Example 1-2c Identify the indicated triangles in the figure. a. isosceles triangles b. scalene triangles Answer:  ABC,  EBC,  DEB,  DCE,  ADC,  ABD Answer:  ADE,  ABE

8. Example 1-4c Find the measures of the sides of  ABC. Classify the triangle by sides. Answer: ; since all 3 sides have different lengths,  ABC is scalene.

9. Find all the missing angles 120 0 b c d 65 0 40 0 e Use Exterior angles Triangle Sum Supplementary angles