We say that two triangles are congruent when (roughly) the sides and angles of one equal the sides and angles of the other. We'll have a single postulate, the so-called Side-Angle-Side Triangle Congruence Postulate. We'll prove two other congruence rules, namely Angle-Side-Angle and Side-Side-Side.
Perhaps the most useful result proven in the chapter is the Isosceles Triangle Theorem. It says that in a triangle with a pair of equal sides, the angles opposite those equal sides are themselves equal.
4.1 Polygon Congruence
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4.2 SAS Congruence
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4.3Â The Isosceles Triangle Theorem and its Converse
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4.4 SSS Congruence
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4.5 ASA Congruence
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4.6 Symmetry
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