McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
4. Proving Triangles Congruent-ASA, AAS
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Exercise 10 Page 368

Identify the pair of vertical angles. Use the Alternate Interior Angles Theorem to determine the second pair of congruent angles.

Statements
Reasons
1.
MS ∥ RQ
1.
Given
2.
∠ PMS ≅ ∠ PRQ
2.
Alternate Interior Angles Theorem
3.
∠ SPM ≅ ∠ QPR
3.
Vertical Angles Theorem
4.
MS ≅ RQ
4.
Given
5.
△ MSP ≅ △ RQP
5.
Angle-Angle-Side (AAS) Congruence Postulate
Practice makes perfect

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
Reasons
1.
MS ∥ RQ
1.
Given
2.
∠ PMS ≅ ∠ PRQ
2.
Alternate Interior Angles Theorem
3.
∠ SPM ≅ ∠ QPR
3.
Vertical Angles Theorem
4.
MS ≅ RQ
4.
Given
5.
△ MSP ≅ △ RQP
5.
Angle-Angle-Side (AAS) Congruence Postulate