2.2.2 Geometric Proof (continued) Example 3 Writing a Two-Column Proof from a Plan Another example of a theorem is the Right Angle Congruence Theorem, which states that all right angles are congruent. This theorem is proven in the example below.
The only given information in the conjecture proven here is that ∠ C and ∠ D are right angles. The conjecture’s conclusion (the statement to be proven) is that ∠ C ≅ ∠ D . Begin by making a plan for the two-column proof. Think of the proof as a puzzle where the first piece is the given information and each subsequent piece depends on the previous piece (or pieces). So, use the given information to deduce new information. And then assume that the new information is true and deduce new information from that assumption.
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