Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
6. Proving Geometric Relationships
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Exercise 17 Page 112

See solution.

Practice makes perfect

We are asked to complete the given flowchart proof.

To fill in the blank spaces in the proof, let's begin by looking at the given information and the desired outcome of the proof. Given:& ∠ 1≅ ∠ 3 Prove:& ∠ 2≅ ∠ 4 Note that the proof corresponds to the given diagram.

We will take a look at the statements that need to be completed one at a time.

Missing Information (a.)

To prove that ∠ 2≅ ∠ 3, we will combine the results from the previous steps. From step two we know that ∠ 1 ≅∠ 2. Also, we are given that ∠ 1≅ ∠ 3. By the Transitive Property of Congruence, we obtain that ∠ 2 ≅ ∠ 3. ∠ 1≅ ∠ 2 ∠ 1≅ ∠ 3 ⇒ ∠ 2 ≅ ∠ 3 Therefore, in the flowchart, we can justify that ∠ 2 ≅ ∠ 3 with the Transitive Property of Equality. \begin{gathered} \underline\textbf{Statement}\\ \angle 2 \cong \angle 3 \\ \textbf{a. }\underline{\text{Transitive Property of Congruence}} \end{gathered}

Missing Information (b.)

To complete the last information, we will again use the Transitive Property of Congruence. From the third step, we know that ∠ 2≅ ∠ 3. In the second step, we also obtained that ∠ 3≅∠ 4. Therefore, by the Transitive Property of Congruence, we conclude that ∠ 2≅∠ 4. ∠ 2≅ ∠ 3 ∠ 3≅ ∠ 4 ⇒ ∠ 2 ≅ ∠ 4 Again, the Transitive Property of Congruence justifies the statement. \begin{gathered} \underline\textbf{Statement}\\ \angle 2 \cong \angle 4 \\ \textbf{b. }\underline{\text{Transitive Property of Congruence}} \end{gathered}

Flowchart Proof

Let's consider one more time the given information and the desired outcome of the proof. Given:& ∠ 1≅ ∠ 3 Prove:& ∠ 2≅ ∠ 4 We will now write the complete flowchart proof.

Two-column Proof

Finally, we will use the flowchart proof to write a two-column proof. Recall that a two-column proof has numbered statements and corresponding reasons organized in a two-column table.

Statements
Reasons
1.
∠ 1 ≅ ∠ 3
1.
Given
2.
∠ 1 ≅ ∠ 2, ∠ 3 ≅ ∠ 4
2.
Vertical Angles Congruence Theorem
3.
∠ 2 ≅ ∠ 3
3.
a. Transitive Property of Congruence
4.
∠ 2 ≅ ∠ 4
4.
b. Transitive Property of Congruence