Unit 6 · Similarity and Dilations

6.6Proportional Segments in Triangles

Quick Answer

The Triangle Proportionality Theorem states that a line parallel to one side of a triangle divides the other two sides proportionally. The converse is also true.

Essential Question

How does a line parallel to one side of a triangle create proportional segments, and how can you use this to find missing lengths?

Learning Goals

  • 1State the Triangle Proportionality Theorem.
  • 2Apply the theorem to find missing segment lengths.
  • 3State and apply the converse.
  • 4Use the theorem in multi-step problems.

Key Vocabulary

Triangle Proportionality Theorem

A line parallel to one side of a triangle divides the other two sides proportionally.

Proportional segments

Segments whose lengths form equal ratios.

Full lesson content coming soon

Worked examples, guided practice problems, a workbook, quiz, and downloadable PDF resources will be added to this lesson in Phase 2. The learning goals and vocabulary above reflect the complete lesson scope.