1. 4-5 Isosceles and Equilateral Triangles
Objective: use and apply properties of isosceles triangles

2. What is an Isosceles Triangle?
Isosceles triangle: A triangle with at least two congruent sides
Legs: The congruent sides of an isosceles triangle
Base: The “other” side not counting as the two congruent sides
Vertex angle: The angle included by the two congruent sides
Base angles: The Angles that include the Base

4. Ex 1: Solve for Variable
Solve for each variable. a) b)

5. Ex 1B: Solve for Variable
c) d)

6. Ex 1C: Solve for Variable

7. Try These
f) g) h)

8. Ex 2: Apply Concepts Triangle RST is an isosceles triangle.
R is the vertex angle, RS = x + 7, ST = x – 1, and RT = 3x – 5.
Find x, RS, ST, and RT.

9. Terminology Reminders
Equilateral triangle: triangle whose sides are all congruent
Postulate (axiom): accepted statement of fact
Theorem: conjecture that is proven
New term
Corollary: statement that follows directly from a theorem

11. Example 2: Solve for each variable. a) b)

12. Try these. c) d)