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.

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 Assignment from the Workbook pg 181 #1 – 6 pg 183 #3, 4, 6 – 10 (Honors also #5) Do not round answers! Leave answers as radicals or fractions where necessary. Due Thursday 11/17 for periods 1, 5, & 7 Due Friday 11/18 for periods 2, 4, & 6