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Head First 2D Geometry by Dawn Griffiths, Stray

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a pizza, no ma
tter
how you slic
e i
t.
lining up
81º
If we had a pair of right angles, they would add
up to 90º + 90º = 180º.
Our pair of mystery angles make up the same
total angle as a pair of right angles, so
aº + bº = 180º.
We know that you can always fit a pair of right angles on a
straight line, but what if we don’t have right angles?
What might this pair of mystery angles (a and b) from our
crime scene sketch add up to?
Solution
Angles on a straight line add up to 180º
Whether a half turn is made up of two quarter turns or
lots of different small turns, the total angle of a half turn
is always 180º.
This means that when the angle on a straight line is
divided up into smaller angles we can always be sure that
they add up to 180º.
Ha
lf a p
izza is ha
lf
81º
90º + 9º + 81º = 180º
14 Chapter 1
finding missing angles
Angle Magnets
Fit the loose angle magnets into the gaps to form three complete
straight lines. Some gaps might need more than one magnet to fill them.
60º
64º
48º
Here
Here
Here
55º
14º
132º
80º
65º
22º
Y
ou might need t
o try a
f
ew dif
f
er
ent combina
tions,
so don’t be s
hy!
you are here 4 15
angle magnets solution
Angle Magnets Solution
Fit the loose angle magnets into the gaps to form three complete straight lines.
60º
64º
48º
Here
Here
Here
55º
14º
132º
80º
65º
22º
60º
64º
48º
132º
55º
65º
22º
80º
14º
60º + 55º + 65º = 180º
64º + 22º + 80º + 14º = 180º
132º + 48º = 180º
16 Chapter 1

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