Download 4-5 Isosceles and Equilateral Triangles

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
e)
Try These
f)
h)
g)
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)