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Learn about the properties and theorems of isosceles and equilateral triangles, including the Isosceles Triangle Theorem and the proof, the Converse of Isosceles Triangle Theorem, and the Corollaries.
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Isosceles Triangle – Triangle with two congruent sides. • The congruent sides are the legs. • The third side is the base. • The two legs form the vertex angle. • The other two angles are the base angles. Legs of an isosceles triangle are congruent. Base angles of an isosceles triangle are congruent.
Isosceles Triangle Theorem If two sides of a triangle are congruent, then the angles opposite those sides are congruent.
Proof of Isosceles Triangle Theorem Given: Prove: This proof requires an auxiliary line.
Converse ofIsosceles Triangle Theorem If two angles of a triangle are congruent, then the sides opposite those angles are congruent.
Theorem If a line bisects the vertex angle of an isosceles triangle, then the line is also the perpendicular bisector of the base.
Corollary – A theorem that can be proved using another theorem.
Corollary If a triangle is equilateral, then the triangle is equiangular.
Corollary If a triangle is equiangular, then the triangle is equilateral.