4'3 Isosceles and Equilateral Triangles 111407

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4.3 Isosceles and Equilateral Triangles11/14/07

• Legs the congruent sides of an isosceles
  triangle.
• Base the other side of an isosceles triangle.
• Base angles - two angles at the base of the
  triangle.

Leg
Leg
Base Angles
Base
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Base Angles Theorem

• If two sides of a triangle are congruent, then
  the angles opposite them are congruent.
• If AB AC, then C B.

A
C
B
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Use the Base Angles Theorem

• Find the m 1.
• The m 1 is 52.

A
1
52
C
B
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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 AC AB.

A
C
B
5
Use the Converse of the Base Angles Theorem

• Find the value of x.

A
12
x 3
B
C
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Equilateral Theorem

• If a triangle is equilateral, then it is
  equiangular.
• If AB AC BC, then A B C

A
C
B
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Equiangular Theorem

• If a triangle is equiangular, then it is
  equilateral.
• If B C A, then AB AC BC

A
C
B
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Find the side length of an Equiangular Triangle
A
C
B

• Find the length of AC
• 3x 2x 10
• X 10
• 3(10) 30

A
3x
C
B
2x 10
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More Practice!!!

• Textbook p. 188 189 7 15 odd, 17 - 25 odd
• Homework worksheet 4.3