An Introduction to Quadrilaterals

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An Introduction to Quadrilaterals

• by Carol Edelstein

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Definition

• Polygon a closed, straight-sided, plane figure.

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Definition

• Angle two rays that meet at a common end point.

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Definition

• Degree a unit of measurement of an angle,
  represented by the symbol º.

90º
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Definition

• Diagonal a line segment joining two
  non-adjacent vertices of a polygon.

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Definition

• Quadrilateral a polygon with 4 angles and 4
  straight sides.

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Special Quadrilaterals
Parallelograms opposite sides are parallel and
congruent.

• Rectangles a parallelogram with all angles
  90.
• Squares a rectangle with all sides equal .
• Rhombus a parallelogram with all sides equal.

Trapezoid one set of sides are parallel.
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Venn Diagram Persective of Quadrilaterals
Quadrilaterals 4 sided polygon

Parallelograms (opposite sides are parallel and
congruent).
Rhombus
Rectangle
Square
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Quadrilateral Family
parallelogram
rectangle
trapezoid
rhombus
quadrilateral
square
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Property of Quadrilaterals

• The sum of all the interior angles equals 360º.

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Property of Quadrilaterals

• Why is the sum 360º ?
• Well, if you choose a vertex you can only
  draw one diagonal. This one diagonal splits
  the quadrilateral into two triangles.
• Since the sum of the internal angles of a
  triangle are 180 degrees, a quadrilateral has 360
  degrees (2 x 180 º ).

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Property of Quadrilaterals

• The sum of all the interior angles equals 360º
  degrees.

65º
65º
65º
115º
115º
115º

115º
65º
360º
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What is the missing angle?
90º
90º
90º
90º
90º
?

90º
90º
?
360º
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What is the missing angle?
70º
70º
70º
70º
110º
?
110º
?
110º

360º
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What is the missing angle?
65º
65º
65º
?
115º
115º
115º
65º
?

360º
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What is the missing angle?
60º
81º
104º
?
104º
115º
?

81º
60º
360º
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Congratulations and good job!

• Now you know that
• A quadrilateral is a 4-sided polygon.
• There are many types of quadrilaterals.
• Classification depends on how many sets of sides
  are parallel, the length of the sides and the
  measure of the interior angles.
• The sum of the interior angles of a quadrilateral
  is 360º.