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Head First 2D Geometry by Dawn Griffiths, Stray

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working backward is fair game
Work backward from area to find butt-space
Normally, you’re given the lengths of the sides of a shape and you
push them through a couple of formulas to get area and perimeter:
Side
length
Perimeter
Start
Area
formula
Perimeter
formula
Area
Usuall
y this is
wha
t y
ou’r
e given.
Often you’r
e aiming
f
or one of these.
But in this case, you know your hot tub area, and you need to find
the length of the sides that would give that area, so you can use
them to find the perimeter (butt-space). To do this you need to work
backward.
Side
length
Perimeter
Start
Area
formula
Perimeter
formula
Area
W
e know the area
of our hot tub.
W
e need t
o find the
side length firs
t.
T
his is our goa
l.
284 Chapter 7
regular polygons
Use any formula you know for area of a square to find the side lengths of the square hot
tub with 6 square meters area.
Then use the side length to find the perimeter.
If each butt requires 0.5 meters of perimeter, how many butts fit in this square hot tub?
6m
2
Reviewing isn’t cheating! Quads
area formulas: page 272.
you are here 4 285
exercise solution
286 Chapter 7
Area of a square = side length x side length
If you had width x height
that w
orks t
oo—but in a
squar
e the width and height
ar
e the same so i
t’s ev
en easi
er!
Perimeter of a square = 4s
Perimeter = 4 x 2.45 = 9.8 meters
Each butt takes 0.5 meters
total butts = 9.8 = 19.6 butts
0.5
2.45 meters = s
6 = s
6 = s
2
Length of
each side.
Uni
ts help y
ou keep
track of wha
t each
Use any formula you know for area of a square to find the side lengths of the square hot
tub with 6 square meters area.
Then use the side length to find the perimeter.
If each butt requires 0.5 meters of perimeter, how many butts fit in this square hot tub?
6m
2
number means.

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