Formulas for Geometry

Mr. Ryan

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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Perimeter

•Triangles have 3 sides…add up each sides length.

8 8 8 8+8+8=24 The Perimeter is 24 Free powerpoint template: www.brainybetty.com

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Perimeter

•A square has 4 sides of a fence

12 12 12 12 Free powerpoint template: www.brainybetty.com

12+12+12+12=48 6

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 Free powerpoint template: www.brainybetty.com

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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 Free powerpoint template: www.brainybetty.com

20 10

Other shapes

•Just add up EACH segment

10 8 sides, each side 10 so 10+10+10+10+10+10+10+10=80 Free powerpoint template: www.brainybetty.com

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Odd shapes

• Count ALL sides • Remember if one side blank, it’s equal to its opposite

25+25=50 (for Length) 15+5+15+5=40 (for Width) 5 15 25 Perimeter=90 Free powerpoint template: www.brainybetty.com

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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 3 2 units (ft, in, m) Free powerpoint template: www.brainybetty.com

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Area of Squares/Rectangles •Length x Width=Area

2 Length(2) xWidth(2) = 4 square units Free powerpoint template: www.brainybetty.com

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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)

5 Height (width) The diagonal line is NOT the height!!!

8 BASE (length) Base 8 x Height 5 = Area 40 Free powerpoint template: www.brainybetty.com

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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 Free powerpoint template: www.brainybetty.com

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Different Names/Same idea •Length x Width = Area •Side x Side = Area •Base x Height = Area

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Area of a Triangle

•½ Base x Height = Area •(It’s ½ because ½ of the “square” is missing)

Height 5 Base 8 Base Height ½ Base x Height = Area ½ (8) x 5 = Area 4 x 5 = 20 Free powerpoint template: www.brainybetty.com

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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 Free powerpoint template: www.brainybetty.com

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Area of a circle

•Area = piR^2 •Pi = 3.14 and R=Radius

5 Radius Area=3.14 x (5 x 5) Perimeter = 3.14 x 10 Free powerpoint template: www.brainybetty.com

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You’re Done

•Squares, rectangles and parallelograms area are almost the same (LxW) •Triangles are ½ cause your missing ½ •Circles have fancy names, but just follow the formula

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

•For most tests you will have the formulas given to you. Just remember which one to use for which shape and you’ll do fine.

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This powerpoint was kindly donated to www.worldofteaching.com

http://www.worldofteaching.com

is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching.

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