- #1
PingPong
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Homework Statement
Below is a sketch for a proof that for any distinct points A and B, there is always a point X between them:
Take P not on [tex]\overleftrightarrow{AB}[/tex] and Q with P between B and Q. Now take R with Q between A and R. The Pasch axiom shows that [tex]\overleftrightarrow{RP}[/tex] crosses AB.
Write down justifications for the steps below:
1) Why is there P not in [tex]\overleftrightarrow{AB}[/tex]?
2) Why is there Q with P between B and Q?
3) Why is Q not equal to A?
4) Why is there R with Q between A and R?
5) Why is R not equal to P?
6) Why is B not on [tex]\overleftrightarrow{RP}[/tex]?
7) Why is A not on [tex]\overleftrightarrow{RP}[/tex]?
8) Why is Q not on [tex]\overleftrightarrow{RP}[/tex]?
9) Why does [tex]\overleftrightarrow{RP}[/tex] not cross AQ?
Homework Equations
The Hilbert axioms for plane geometry.
The Attempt at a Solution
I've been able to get the first 5 steps which are quite easy. But 6-8 have been giving me trouble. I can see that they're important because they're setting up using the Pasch axiom, but I can't figure out why they are true based by starting with the axioms.
For 6, I can see (if I draw a picture) then R=Q, which means that R is between A and itself (which can't be). So I can intuitively see that they don't work, but I'm not sure how to put it together.
Any help please? Thanks in advance.