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The Isosceles Triangle Theorems
Section 4-4 The Isosceles Triangle Theorems
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Isosceles Diagram: Vertex Angle Base
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Description of Parts: Legs: the congruent sides Base: non-congruent side; opposite the vertex angle Base Angles: the two ’s formed by the base and one of the congruent sides Vertex Angle: formed by the sides
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The Isosceles Triangle Theorem
If two sides of a triangle are congruent, then the angles opposite those sides are congruent. A B C So…
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In other words, Base angles of an isosceles triangle are congruent!
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An equilateral triangle is also equiangular.
Corollaries: An equilateral triangle is also equiangular. An equiangular triangle is also equilateral. An equilateral triangle has three 60 degree angles.
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Corollary: The bisector of the vertex angle of an isosceles triangle is perpendicular to the base at its midpoint. A B C M
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cONVERSE Isosceles Triangle Theorem
If two angles of a triangle are congruent, then the sides opposite those angles are congruent. A B C So…
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