Common Core: High School - Geometry : Parallelogram Proofs

Study concepts, example questions & explanations for Common Core: High School - Geometry

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All Common Core: High School - Geometry Resources

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Example Questions

Example Question #21 : Prove Parallelogram Theorems: Ccss.Math.Content.Hsg Co.C.11

Prove that since this quadrilateral has two pairs of opposite congruent angles it is a parallelogram.

Screen shot 2020 08 20 at 9.48.56 am

Possible Answers:

Proof:

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Proof:

Screen shot 2020 08 20 at 9.51.28 am

Proof:

Screen shot 2020 08 20 at 9.50.12 am

Correct answer:

Proof:

Screen shot 2020 08 20 at 9.50.51 am

Explanation:

Screen shot 2020 08 20 at 9.49.06 am

Thus, we have shown that if a quadrilateral has two pairs of opposite congruent angles, it is a parallelogram.

Example Question #151 : Congruence

Prove the following parallelogram has two pairs of opposite congruent angles.

Screen shot 2020 08 20 at 10.02.30 am

Possible Answers:

Proof:

 is a parallelogram (given)

We can add the line  across the diagonal

Screen shot 2020 08 20 at 10.04.42 am

 is parallel to 

 is parallel to  (definition of a parallelogram)

 (alternate interior angles)

 is a common side between  and 

 (By Angle-Side-Angle Theorem)

 (corresponding parts of congruent triangles)

 (Addition of equalities)

 (Angle Addition Postulate)

Therefore  and 

Proof:

 is a parallelogram (given)

We can add the line  across the diagonal

Screen shot 2020 08 20 at 10.04.42 am

 is parallel to 

 is parallel to  (definition of a parallelogram)

 (alternate interior angles)

 is a common side between  and 

 (By Angle-Side-Angle Theorem)

Because the triangles are congruent we can assume:

Therefore  and 

Proof:

 is a parallelogram (given)

We can add the line  across the diagonal

Screen shot 2020 08 20 at 10.04.42 am

 is parallel to 

 is parallel to  (definition of a parallelogram)

 (corresponding angles)

 is a common side between  and 

 (By Angle-Side-Angle Theorem)

 (corresponding parts of congruent triangles)

 (Addition of equalities)

 (Angle Addition Postulate)

Therefore  and 

Correct answer:

Proof:

 is a parallelogram (given)

We can add the line  across the diagonal

Screen shot 2020 08 20 at 10.04.42 am

 is parallel to 

 is parallel to  (definition of a parallelogram)

 (alternate interior angles)

 is a common side between  and 

 (By Angle-Side-Angle Theorem)

 (corresponding parts of congruent triangles)

 (Addition of equalities)

 (Angle Addition Postulate)

Therefore  and 

Explanation:

Statement                                                                            Reasoning

 is a parallelogram.                                           This is given in the problem.

We can add the line  across the diagonal                   Connecting any two points make a line, so this is a valid line we can add.

 Screen shot 2020 08 20 at 10.03.17 am

 is parallel to 

 is parallel to   We know this to be true according to the definition of a parallelogram.

 Line  is a transversal line intersection two parallel lines. We could extend lines  and  or lines  and  to make this relationship more clear. Alternate interior angles are formed by this transversal line.

Screen shot 2020 08 20 at 10.03.56 am

 is a common side between  and 

 We are able to use the Angle-Side-Angle Theorem because we have one congruent side between these two triangles, , and two pairs of congruent angles, 

 Congruent triangles have congruent corresponding parts by definition

 Because these angles are congruent they are also equal

 Since  we can add one of these angles to each side and still keep the equation balanced and equal

 The Angle Addition Postulate says that two side by side angles create a new angle whose measure is equal to their sum

  We are simply substituting these equalities into the equation 

 Equal angles are congruent

Therefore  and 

Thus, we have proven that this parallelogram has two pairs of opposite congruent angles.

Example Question #11 : Parallelogram Proofs

Prove the following parallelogram has diagonals that bisect each other.

Screen shot 2020 08 20 at 10.34.27 am

Possible Answers:

Proof:

Screen shot 2020 08 20 at 10.36.23 am

Proof:

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Proof:

Screen shot 2020 08 20 at 10.35.58 am

Correct answer:

Proof:

Screen shot 2020 08 20 at 10.35.58 am

Explanation:

Screen shot 2020 08 20 at 10.34.58 am

All Common Core: High School - Geometry Resources

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