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Head First 2D Geometry by Dawn Griffiths, Stray

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finding missing angles
Find one more angle to crack the case
There’s only one unknown angle left on the diagram. Once you’ve
figured out this one you can charge Benny with the shooting for sure.
Find this last mystery angle to complete your investigation
and prove that Benny was the shooter.
How does it fit in with what you’ve already found out?
CRIME SCENE SKETCH
CASE GEO180
(ANGLES AS MEASURED
BUT DRAWING NOT TO
SCALE)
BULLET
PA
TH
MICKY
BENNY
18º
81º
86º
72º
81º 99º
FOOTPRINTS
you are here 4 21
Hmm…something f
unn
y
is going on. It doesn’t
ma
tter how you w
orded
i
t,.as long as y
ou noticed
something didn’t add up.
something funny is going on…
Find this last mystery angle to complete your investigation and
prove that Benny was the shooter.
How does it fit in with what you’ve already found out?
CRIME SCENE SKETCH
CASE GEO180
(ANGLES AS MEASURED
BUT DRAWING NOT TO
SCALE)
BULLET
PA
TH
MICKY
BENNY
FOOTPRINTS
18º
81º
86º
72º
81º 99º
There are 2 different ways to find this
mystery angle—you might have done either one.
1)
2)
Angle c is opposite
this angle here
Angles in a triangle add up to 180º
And vertical angles are equal,
so 81º + 86º + ? = 180º
so ? = 18º
? = 180º - 81º - 86º = 13º
But this doesn’t fit with the
triangle angles:
But this doesn’t fit with the 18º
angle it’s opposite. They should be
equal.
18º + 81º + 86º = 185º
They should add up to 180º.
22 Chapter 1

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