Lesson 4-9: Isosceles and Equilateral Triangles Rigor: Use and apply properties of isosceles and equilateral triangles Relevance: Triangle properties are used in architecture, construction, and art.

Notes: Isosceles Triangles Isosceles triangles have at least 2 ≅ sides. Parts: Isosceles Triangle Theorem – If 2 sides of a triangle are congruent, then the angles opposite them are congruent.

Notes: Isosceles Triangles continued The converse is also true! Isosceles Triangle Theorem Converse: If 2 angles of a triangle are congruent, then the opposite sides are also congruent. We will prove both of these theorems later in the chapter using congruent triangles.

Example: Which theorem proves the statement is true? WVS ≅ S 𝑅𝑇 ≅ 𝑆𝑇

Equilateral Triangle Theorem A triangle is equilateral if and only if it is equiangular. AND

Examples: Applying the triangle theorems

Examples continued: What is CB?

4-9 Classwork and Homework 4-9 Classwork: Core book pg 181 #1 - 6 4-9 Homework: Standard: core book pg 183 #3, 4, 6 – 10 Honors: core book pg 183 #3 – 10 Due Thursday for periods 1, 3, 5 Due Friday for periods 2, 4, 7