1. Triangles Chapter 4

2. 1 2 3 45 What is the sum of the angles inside a triangle? 180º? Prove it m Given A B C Angle Addition Postulate/Definition of a Straight Angle Alternate Interior Angles Theorem and Definition of Angle Congruence Substitution

3. Classifying Triangles by Sides Equilateral - Three congruent sides Isosceles - Two congruent sides Scalene - No congruent sides

4. Equilateral - Three congruent sides Isosceles - Two congruent sides Find the values of x, y, and the measures of the sides of each triangle Be ready to discuss these answers in class

5. Classifying Triangles by Angles Acute - All three angles < 90 º Equiangular - All three angles = 60 º Right - One right angle Obtuse - One obtuse angle

6. Exterior Angle Theorem (you’ll be proving this) 1 2 34 The measure of an exterior angle of a triangle is equal to the sum of the measures of its remote interior angles Remote Interior Angles

7. Third Angle Theorem A B C If two angles of one triangle are congruent to two angles of another triangle, then the third pair of angles are congruent. R P Q If this is true then

8. A B C If two angles of one triangle are congruent to two angles of another triangle, then the third pair of angles are congruent. R P Q Find the values of x, 61º (27x)º (9x 2 )º and Be ready to discuss these answers in class