Chapter 3: Parallel Lines and Triangles

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3.1  Lines in Space

3.2  Parallel Lines and Transversals

Parallel Lines and Transversals

This site defines parallel lines and crossing lines and all of the resulting angles.

3.3  Proving Lines Parallel

Parallel Lines and Transversals

This site defines parallel lines and crossing lines and all of the resulting angles.

3.4  The Triangle Sum Theorem

Triangle Sum Theorem

This site has a demonstration that the sum of the interior angles of a triangle equals 180 degrees.

3.5  Inequalities in Geometry

Triangle Inequalities

This site gives two theorems that deal with triangle inequalities.

Triangle Inequalities

This site shows examples to help students understand triangle inequalities.

3.6  The Triangle Inequality Theorem

Triangle Inequalities

This site gives two theorems that deal with triangle inequalities.

Triangle Inequalities

This site shows examples to help students understand triangle inequalities.