AREA

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AREA
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Area is a measure of two dimensional
spaceLengthWidth
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How to calculate the area of a rectangle.
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Area of a rectangle L x W
W 10 in
L 25 in
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Area 25 x 10 250 square inches
W 10 in
L 25 in
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How to calculate the area of a parallelogram.
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Area of a parallelogram L x H
H 10
L 18
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Cut off a right triangle.
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Translate this triangle to the other side of the
parallelogram.
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Now we have a rectangle. We know how to find the
area of a rectangle L x W
W 10
L 18
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The area of this rectangle is 180.
W 10
L 18
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So, the area of this parallelogram must be 180
also.
H 10
L 18
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How to calculate the area of a triangle.
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Every triangle is half the area of a larger
rectangle.
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Even scalene triangles are half the size of a
larger rectangle.
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It may, however, take some adjusting to see this.
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PRESTO!
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If every triangle is half the area of a larger
rectangle, then the formula for the area of a
triangle isLength x Width ? 2
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However, a triangle really does not have a length
and a width.Rather, triangles have a height and
a base.
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The height of a triangle is always measured from
the highest point of the triangle.
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If you were measuring a persons height, you
would measure from the persons head, not his/her
shoulder.
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If you were measuring the height of this tree,
you would measure from the trees highest point.
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Height
Base
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Height
Base
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Height
Base
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Lets calculate the area of this triangle.
Height 5
Base 6
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The area of this triangle is 1/2 the area of this
rectangle.
5
6
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If the area of this rectangle is 30...
5
6
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Then the area of this triangle is 15.
5
6
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Wow! Do I have to remember all of those formulas?
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Nope! You only have to remember the formula for
a rectangle.
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If you understand that a parallelogram covers the
same area as a rectangle...
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and a triangle covers half the area of a
rectangle,
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then you can always use the formula for a
rectangle!
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Summary

• Area of a rectangle L x W
• Area of a parallelogram L x W
• Area of a triangle L x W ? 2

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Calculate the area of this rectangle.
3 yards
12 yards
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Area 3 x 12 36 sq. yards
3 yards
12 yards
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Calculate the area of this parallelogram.
13 feet
11 feet
7 feet
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Area 7 x 11 77 sq. feet
13 feet
11 feet
7 feet
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Calculate the area of this triangle.
7 cm
5 cm
4 cm
9 cm
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Area 9 x 4 ? 2 18 sq. cm
7 cm
5 cm
4 cm
9 cm
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THE END!