Formulas for Geometry

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Area

Area is the ENTIRE INSIDE of a shape

It is always measured in “squares” (sq. inch, sq ft)

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AREA

Square units means that “that” many squares fit inside that shape (if measured in feet…it’s feet…if meters…it’s meters. In this example the area is 4 square units…note 4 squares fit)

1

2 units (ft, in, m)

2

3

4

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Area of Squares/Rectangles

Length x Width=Area

2

Length(2) xWidth(2) = 4 square units

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Parallelogram Area

Same idea as squares & rectangles, but they change the words to Base (length:bottom of shape) and height (width)

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Parallelogram Area

Area=Base x Height

(Area=length x width)

BASE (length)

Height (width)

8

5

Base 8 x Height 5 = Area 40

The diagonal line is NOT

the height!!!

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Real formula for area of squares

Area= S^2

Area= Side x Side (side squared) (just a different way of saying length x width)

Side one

Side two

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Different Names/Same idea

Length x Width = Area

Side x Side = Area

Base x Height = Area

Slide 20

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Area of a Triangle

½ Base x Height = Area

(It’s ½ because ½ of the “square” is missing)

Base

Height

Height

Base

8

5

½ Base x Height = Area

½ (8) x 5 = Area

4 x 5 = 20

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Area of a Circle

Pi= 3.14

Radius: from center (origin) of circle to ANY side

Area= pi x (Radius x Radius)

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Circumference of a Circle

Perimeter/Circumference = pi x diameter

Pi is always 3.14

Circumference is a fancy name for perimeter

The diameter is a line from one side to the other side of a circle through its origin (It’s twice the radius)

If the radius is 5, then the diameter is 10

Slide 23

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Area of a circle

Area = piR^2

Pi = 3.14 and R=Radius

Radius

5

Area=3.14 x (5 x 5)

Perimeter = 3.14 x 10