Geometric Proofs

9th Grade30 minutes

Learning Objective

I can write a two-column proof to prove geometric theorems.

Key Concepts

A two-column proof includes a statement and a reason for the statement.

If three sides of two triangles are congruent, then the triangles are congruent by the side-side-side postulate.

If two triangles are congruent, then all of their corresponding angles are equivalent.

Practice Questions

This lesson includes 3 practice questions to reinforce learning.

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1. What is the purpose of a two-column proof in geometry?

2. In the video's proof, which congruence postulates were used to prove that segment AC is perpendicular to segment DB?

3. In your own words, describe how the Side-Side-Side (SSS) postulate was applied in the video's proof. Be specific about which segments were used to establish congruence.

Educational Video

Two column proof showing segments are perpendicular | Congruence | Geometry | Khan Academy

Khan Academy

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