4. Proving Triangles Congruent-ASA, AAS
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Identify the pair of vertical angles. Use the Alternate Interior Angles Theorem to determine the second pair of congruent angles.
Statements
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Reasons
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1. MS ∥ RQ
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1. Given
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2. ∠ PMS ≅ ∠ PRQ
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2. Alternate Interior Angles Theorem
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3. ∠ SPM ≅ ∠ QPR
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3. Vertical Angles Theorem
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4. MS ≅ RQ
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4. Given
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5. △ MSP ≅ △ RQP
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5. Angle-Angle-Side (AAS) Congruence Postulate
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We begin by noticing that ∠ SPM and ∠ QPR are vertical angles, and so by the Vertical Angles Theorem we conclude that ∠ SPM ≅ ∠ QPR.
Since MS ∥ RQ and MR is a transversal, by the Alternate Interior Angles Theorem we get that ∠ PMS ≅ ∠ PRQ.
Remember that we also have MS ≅ RQ, and so by applying the Angle-Angle-Side (AAS) Congruence Postulate we get △ MSP ≅ △ RQP. We summarize this proof in the following two-column table.
Statements
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Reasons
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1. MS ∥ RQ
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1. Given
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2. ∠ PMS ≅ ∠ PRQ
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2. Alternate Interior Angles Theorem
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3. ∠ SPM ≅ ∠ QPR
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3. Vertical Angles Theorem
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4. MS ≅ RQ
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4. Given
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5. △ MSP ≅ △ RQP
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5. Angle-Angle-Side (AAS) Congruence Postulate
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