LESSON 6.3 PROVING THAT A QUADRILATERAL IS A PARALLELOGRAM OBJECTIVE: Determine whether a...
Transcript of LESSON 6.3 PROVING THAT A QUADRILATERAL IS A PARALLELOGRAM OBJECTIVE: Determine whether a...
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LESSON 6.3 PROVING THAT A QUADRILATERAL IS A PARALLELOGRAM
OBJECTIVE:Determine whether a quadrilateral is a parallelogram
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Theorem 6.5If the diagonals of a quadrilateral
_______ each other, then the quadrilateral is a parallelogram.
Theorem 6.6If one pair of opposite sides of a
quadrilateral is both _______ and __________, then the quadrilateral is a parallelogram.
Theorems
bisect
parallel
congruent
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Theorem 6.7If both pairs of opposite sides of a
quadrilateral are __________, then the quadrilateral is a parallelogram.
Theorem 6.8If both pairs of opposite angles of a quadrilateral are ___________, then
the quadrilateral is a parallelogram.
Theorems Con’t
congruent
congruent
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EXAMPLE #1Find the values for x and y for which ABCD must be a parallelogram.If the diagonals of quadrilateral ABCD _______ each other, then ABCD is a parallelogram, so
bisect
10x – 24 = 8x + 12 and 2y – 80 = y + 92x – 24 = 12
2x = 36
x = 18
y – 80 = 9 y =
89
If x = 18 and y = 89, then ABCD is a ___________.
parallelogram
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EXAMPLE #2
Determine whether each quadrilateral is a parallelogram. Explain.
a. All you know about the quadrilateral is that only one pair of opposite sides is congruent. Is that enough to prove the quadrilateral is a parallelogram?No, b/c there is no theorem that states only one pair of opposite sides must be congruent to be a parallelogram.
__________________________________________________________________________________________________________________
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EXAMPLE #2
Determine whether each quadrilateral is a parallelogram. Explain.
b. The sum of the measures of the angles in a polygon is (n – 2)180, so the sum of the measures of the angles of a quadrilateral is ___________
Yes, b/c both pairs of opposite angles are congruent, which makes it a parallelogram.
____________________________________________________________________________
If x represents the measure of the unknown angle,
x + 75 + 105 + 75 = ______, so x = _______.
(4 – 2)180 = 360
360 105
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Assignment: pg 307 #1-15, 20-29