1. ISOSCELES TRIANGLES
Section 4-6
spi.3.2.A
Jim Smith
JCHS

2. Isosceles triangles have at least
2 congruent sides
Vertex angle
Leg
Leg
Base angle
Base angle
Base

3. | | If 2 sides of a triangle are congruent
then the angles opposite them are congruent | |

4. X
30° | | | | X X
70°
70°
180 – 30 = 150°
X = 150 2
X = 75°
X = 180 – 70 – 70
X = 40°
X + X + 30 = 180°
2X + 30 = 180
2X = 150
X = 75°
X = 180
X = 180
X = 40°

5. X = 10 The converse is also true
If 2 angles of a triangle are congruent,
then the sides opposite them are congruent
X = 10 10 X 7

6. IF ‹ EDC = 120° Find : ‹ ABE = ‹ A = ‹ BED = ‹ EDB = 23° ‹ C = 134°|
| | A B C D E
IF ‹ EDC = 120°
Find :
‹ ABE =
‹ A =
‹ BED =
‹ EDB =
‹ C =
35°
22°
23°
134°
79°
104°
23°
120 – 79 = 41°

7. ‹1 = 62° ‹2 = ‹3 = 56° ‹5 = 31° ‹6 = IF ‹4 = 118° , FIND B | A C D 1 2

8. Equilateral triangles are special isosceles triangles.
60° | |
60°
60° |