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Warm-up
Finish the back page of your homework!!!
 15 minutes if you are done early you need
to compare answers with a
neighbor/friend

Warm-up

Label the following triangles by their sides
and angles
Today
Warm-up
 Quiz
 Objective
 Notes
 Practice Problems

Geometry 4.3: Isosceles and
Equilateral Triangles
Objective: _______________________________
_____________________________
Parts of an Isosceles Triangle

Legs: Congruent Sides

Base: Non-congruent side

Base Angles: 2 angles
at the base of the triangle
Isosceles Triangle
1.
Use a ruler to draw a isosceles triangle on
patty paper
1. The congruent sides need to be 4 inches long
Draw an arc on one of the base angles.
3. Fold the patty paper so that the crease is
down the middle of the triangle going
trough the base.
4. Line up the angles
 What do you notice about the to base
angles?
2.
Equilateral Triangles
1.
Use a ruler to draw a Equilateral triangle on
patty paper
1. All of the sides need to be 4 inches long
1.
2.
3.
Start with the base, at the two inches put a mark
Draw a line perp. to the base from the 2 inch mark
Draw the two other sides 4 inches long touching that
middle line.
Draw an arc the one of the angles.
Fold the patty paper so that the crease is down
the middle of the triangle.
4. Line up the angles.
5. Try folding again using a different set of angles.
 What do you notice about the to angles?
2.
3.

Base Angle Theorem: If two sides of a
triangle are congruent, then the angles
opposite them are congruent.
If AB = AC, then __________
Practice:

Converse of the Base Angles Theorem: If two
angles of a triangle are congruent, then the
sides opposite them are congruent.
If <B = <C, then _____
Practice

Equilateral Triangle Theorem: If a triangle
is equilateral, then it is equiangular.

Equiangular Theorem: If a triangle is
equiangular then it is equilateral.
Practice