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Head First 2D Geometry by Dawn Griffiths, Stray

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T
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e
d
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th is ac
tua
lly a 10-sided
p
ol
ygon known as a decagon.
use triangles to find polygon areas
Chop the polygons into triangles
When you investigated the pizza area formula back in
Chapter 5, you created a series of polygons by chopping
the pizza into triangular slices.
Any regular polygon can be divided into the same number
of congruent triangles as the polygon has sides.
Hexagon: 6 sides,
6 tr
iangles
Oc
tagon: 8 sides,
8 tr
iangles
So, if we know the area of one of those triangles,
we can easily find the area of the whole polygon.
302 Chapter 7
A nice idea. Except we don’t know
anything about those triangles. We
don’t know base and height or side lengths!
Without those we can’t find the area. Even
Hero’s formula can’t rescue this one....
That’s true. We don’t have enough
information.
To use either technique we know for finding triangle area
we’re going to need to know more about these triangles.…

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