All Common Core: High School - Geometry Resources
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.
Proof:
Proof:
Proof:
Proof:
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.
Proof:
is a parallelogram (given)
We can add the line across the diagonal
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
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
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
Proof:
is a parallelogram (given)
We can add the line across the diagonal
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
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.
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.
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.
Proof:
Proof:
Proof:
Proof:
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