Finding Area and Perimeter of Polygons

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Finding Area and Perimeter of Polygons
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Area

• Definition
• The number of square units needed to cover a
  surface. (INSIDE)
• Length x width

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Perimeter

• Definition
• The sum of the length of all the sides of a
  polygon.

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Base

• Definition
• A side or face of a figure on which the figure
  stands.

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Height

• Definition
• The distance from the bottom to the top of a
  figure.

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Width

• Definition
• How wide a figure is from side to side.

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Length

• Definition
• The measure of the distance across an figure.

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How to findArea.
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Finding area of an irregular figure

• Box the object in then count the length and the
  width of the box.
• Example
• Length 4
• Width 5

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Finding area of an irregular figure

• Hint Length x widtharea
• What is the area of the box?

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Finding area of an irregular figure

• Hint Length x widtharea
• What is the area of the box?
• Right!
• 4x520

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Finding area of an irregular figure

• How many squares are there in the box that are
  not shaded?

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Finding area of an irregular figure

• How many squares are there in the box that are
  not shaded.
• Right!
• 6 squares

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Finding area of an irregular figure

• The area of the object is the area of the box
  (20) minus the squares that are are not shaded
• (6).

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Finding area of an irregular figure

• The area of the object is
• 20-6 14
• The area of the irregular figure is 14.
• This method can be used instead of counting all
  the squares.

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How to findperimeter.
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Finding perimeter of a figure

• Perimeter distance around an object.
• In this case the Box.

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Finding perimeter of a figure

• For this figure the length is 4 and the width is
  5. You have two 4s and two 5s.
• The perimeter is
• 2x4 2x5 perimeter

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Finding perimeter of a figure

• Multiply first, then add
• The perimeter is
• 2x4 2x5 perimeter
• 8 10

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Finding perimeter of a figure

• Multiply first, then add
• The perimeter is
• 2x4 2x5 perimeter
• 8 10 18
• The perimeter of the box is 18.

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Finding perimeter of a figure

• 18 is the perimeter of the box. So what?
• We want to know the perimeter of the figure.Do we
  know the perimeter of the figure?

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Finding perimeter of a figure

• Yes, the perimeters are the same.
• The blue is the perimeter of the figure.
• The red is the perimeter of the box.

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Finding perimeter of a figure
That trick does not work all the time. Sometimes
you may have to count the side and add. What is
the perimeter of this figure?
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Finding perimeter of a figure
What is the perimeter of this figure?
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Finding perimeter of a figure
Right 20! 10 on top and bottom 10 on the right
and left
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Now Go to

• www.shodor.org/interactivate/activities/perimeter/