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

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

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

Ex 1B: Solve for Variable c) d)

Ex 1C: Solve for Variable

Try These f) g) h)

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.

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

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

Try these. c) d)