Isosceles Triangles

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Isosceles Triangles

• Chapter 4 Day 11

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Properties of Isosceles Triangles
Vertex Angle
Base Angles
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Isosceles Triangle Theorem

• If two sides of a triangle are congruent then the
  angles opposite those sides are congruent.
• Example
• Given
• Conclusion

B A C
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Isosceles Triangle Theorem

• Write a two-column proof.
• Given AB CB BD, ? ACB ? ? BCDProve ? A
  ? ? D

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Find the measure of a missing angle.
m ? BAC 75
75
120
30
30
30
75
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Converse of the Isosceles Triangle Theorem

• If two angles of a triangle are congruent then
  the sides opposite those angles are congruent.
• Example
• Given
• Conclusion

B A C
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Congruent Segments and Angles

• Name two congruent angles
• Name two congruent segments

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Check for Understanding