# Download Isosceles Triangle: * A triangle with at least two congruent sides

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```October 28, 2013
Geom
4-6 Isosceles Triangles
Isosceles Triangle:
* A triangle with at least two congruent sides.
Vertex Angle:
* The angle formed by the 2 congruent
sides.
Base Angles:
* The 2 angles formed by the base and 1 of
the congruent sides.
Legs:
* The two congruent sides.
Vertex Angle
Leg
Leg
Base Angle
Base
October 28, 2013
Isosceles Triangle Theorem:
* If 2 sides of a triangle are congruent, then
the angles opposite those sides are
congruent.
* Base angles are congruent.
B
A
C
If AB ≅CB,
then ∠A ≅ ∠C
Isosceles Triangle Converse Theorem:
* If 2 angles of a triangle are ≅, then the
sides opposite those ∠'s are ≅.
E
D
If ∠D
F
≅ ∠F, then DE ≅ FE.
October 28, 2013
Properties of Equilateral Triangles:
* The Isosceles Triangle Theorem will apply
to the equilateral triangle.
* Base angles are congruent.
Corollary:
* A triangle is equilateral iff it is equiangular.
Corollary:
* Each angle of an equilateral triangle is 60˚.
1. If DE ≅
CD, BC ≅ AC, and m∠CDE =
120˚, what is the measure of ∠BAC?
D
C
B
E
A
2. a. Name 2 congruent
angles.
b. Name 2 congruent
segments.
M
P
L
N
October 28, 2013
3. Take the figure shown and Draw EJ so that
EJ bisects ∠2, and J lies on FG.
∆EFG is equilateral,
EH bisects ∠E.
E
12
Find the following:
a. m ∡HEJ
b. m ∡ EJH
c. m ∡EJG
F
(15x˚)
H
4 - 6 Isosceles Triangles
pg. 219 - 221
#1, 4 - 6, 9 - 11, 15 - 18, 23 - 28,
35 - 37, 46, 52, 54
G
```
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