Formulas for Geometry

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Formulas for Geometry

Mr. Ryan

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Don’t Get Scared!!!

Evil mathematicians have created formulas to save you time. But, they always change the letters of the formulas to scare you!

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Perimeter

Any shape’s “perimeter” is the outside of the shape…like a fence around a yard.

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Perimeter

To calculate the perimeter of any shape, just add up “each” line segment of the “fence”.

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Free powerpoint template: www.brainybetty.com

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Perimeter

Triangles have 3 sides…add up each sides length.

8

8

8

8+8+8=24

The Perimeter is 24

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Perimeter

A square has 4 sides of a fence

12

12

12

12

12+12+12+12=48

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Perimeter

Sometimes, problems may only give you two measurements for a square or rectangle.

No problem…use the formula for squares/rectangles (only!)

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Remember

Squares ALL sides are equal…so if they give you one side, you know ALL the sides

Length=the Largest side

If they “leave” numbers out, they are equal to their opposite side. If they give you the bottom of a square/rectangle type shape then the top is the same

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The Same!!

If the bottom is 15…the top is…

15

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Square/Rectangle Formula

Perimeter=2(Length+Width)

P= 2(25+14) P=2(20+20)

P= 50+28 P=40+40

P= 78 P=80

14

25

20

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Other shapes

Just add up EACH segment

10

8 sides, each side 10 so 10+10+10+10+10+10+10+10=80

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Odd shapes

Count ALL sides

Remember if one side blank, it’s equal to its opposite

25

15

5

25+25=50 (for Length)

15+5+15+5=40 (for Width)

Perimeter=90

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