Formulas for Geometry

1
Formulas for Geometry

• Mr. Ryan

Visit www.worldofteaching.com for more free
powerpoints
2
Dont Get Scared!!!

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

3
Perimeter

• Any shapes perimeter is the outside of the
  shapelike a fence around a yard.

4
Perimeter

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

5
Perimeter

• Triangles have 3 sidesadd up each sides length.

8
8
88824 The Perimeter is 24
8
6
Perimeter

• A square has 4 sides of a fence

12
12
12
1212121248
12
7
Perimeter

• Sometimes, problems may only give you two
  measurements for a square or rectangle.
• No problemuse the formula for squares/rectangles
  (only!)

8
Remember

• Squares ALL sides are equalso if they give you
  one side, you know ALL the sides
• Lengththe 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

9
The Same!!

• If the bottom is 15the top is

15
10
Square/Rectangle Formula

• Perimeter2(LengthWidth)
• P 2(2514) P2(2020)
• P 5028 P4040
• P 78 P80

14
20
25
11
Other shapes

• Just add up EACH segment

10
8 sides, each side 10 so 10101010101010108
0
12
Odd shapes

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

15515540 (for Width)
252550 (for Length)
5
15
Perimeter90
25
13
Area

• Area is the ENTIRE INSIDE of a shape
• It is always measured in squares (sq. inch, sq
  ft)

14
AREA

• Square units means that that many squares fit
  inside that shape (if measured in feetits
  feetif metersits meters. In this example the
  area is 4 square unitsnote 4 squares fit)

1
2
3
4
2 units (ft, in, m)
15
Area of Squares/Rectangles

• Length x WidthArea

2
Length(2) xWidth(2) 4 square units
16
Parallelogram Area

• Same idea as squares rectangles, but they
  change the words to Base (lengthbottom of shape)
  and height (width)

17
Parallelogram Area

• AreaBase x Height
• (Arealength x width)

The diagonal line is NOT the height!!!
5
Height (width)
8
BASE (length)
Base 8 x Height 5 Area 40
18
REAL formula for area of squares

• Area S2
• Area Side x Side (side squared) (just a
  different way of saying length x width)

Side one
Side two
19
Different Names/Same idea

• Length x Width Area
• Side x Side Area
• Base x Height Area

20
Area of a Triangle

• ½ Base x Height Area
• (Its ½ because ½ of the square is missing)

Height
5
Base
8
Height
½ Base x Height Area ½ (8) x 5
Area 4 x 5 20
Base
21
Area of a Circle

• Pi 3.14
• Radius from center (origin) of circle to ANY
  side
• Area pi x (Radius x Radius)

22
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 (Its
  twice the radius)

If the radius is 5, then the diameter is 10
23
Area of a circle

• Area piR2
• Pi 3.14 and RRadius

5
Radius
Perimeter 3.14 x 10
Area3.14 x (5 x 5)
24
Youre 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

25
?

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