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4.1 Triangle Sum Theorem
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The sum of the measures of the interior angles of a triangle is 180 degrees.
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4.1 Corollary
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The acute angles of a right triangle are complementary.
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4.2 Exterior Angle Theorem
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The measure of an exterior angle of a triangle is equal to the sum of the measures of the two nonadjacent interior angles.
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4.3 Third Angles Theorem
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If two angles of one triangle are congruent to two angles of another triangle, then the third angles are also congruent.
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4.4 Properties of Triangle Congruence
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Reflexive:
Symmetric:
Transitive:
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4.5 Hypotenuse-Leg (HL) Congruence Theorem
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If the hypotenuse and a leg of a right triangle are congruent to the hypotenuse and a leg of a second right triangle, then the two triangles are congruent.
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4.6 Angle-Angle-Side (AAS) Congruence Theorem
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If two angles and a non-included side of one triangle are congruent to two angles and the corresponding non-included side of a second triangle, then the two triangles are congruent.
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4.7 Base Angles Theorem
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If two sides of a triangle are congruent, then the angles opposite them are congruent.
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4.7 Corollary
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If a triangle is equilateral, then it is equiangular.
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4.8 Converse of the Base Angles Theorem
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If two angles of a triangle are congruent, then the sides opposite them are congruent.
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4.8 Corollary
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If a triangle is equiangular, then it is equilateral.
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