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Head First 2D Geometry by Dawn Griffiths, Stray

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Frank
Jill
Joe
finding missing angles
Something doesn’t add up!
Using the two different methods
for finding the mystery angles
gives us two different results.
And vertically opposite
angles are equal, so ? = 18º
Angles in a triangle add up to
180º so 81º + 86º + ? = 180º
? = 180º - 81º - 86º = 13º
This is not good. The whole investigation
could be compromised by bad math!
Joe: This is a disaster. How can there be two different answers?
It’s totally confusing.
Jill: Benny’s lawyer is gonna have a field day. I don’t believe it.
We’ve got the right guy in custody—it’s obvious he did it—and
we’re gonna have to let him go because of some messed up math!
Can we fix it?
Frank: The weirdest thing is that I’m looking again at the math
for either method and it looks good. I mean—corners on a
triangle always add up to 180 degrees, and vertically opposite
angles are always equal. Those are the rules.
Joe: I knew we were relying too much on these coincidences. My
guess is that these “rules” don’t always actually work!
Jill: I really don’t think that’s what it means. If we haven’t
messed up the calculations then the fact that we got two different
answers simply has to mean something else.…
What do you think it means?
you are here 4 23

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