this post was submitted on 20 Oct 2024
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Math Memes

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[–] [email protected] 0 points 4 weeks ago (8 children)

It's fucking obvious!

Seriously, I once had to prove that mulplying a value by a number between 0 and 1 decreased it's original value, i.e. effectively defining the unary, which should be an axiom.

[–] [email protected] 0 points 3 weeks ago* (last edited 3 weeks ago) (5 children)

So you need to proof x*c < x for 0<=c<1?

Isn't that just:

xc < x | ÷x

c < x/x (for x=/=0)

c < 1 q.e.d.

What am I missing?

[–] [email protected] 0 points 3 weeks ago (4 children)

My math teacher would be angry because you started from the conclusion and derived the premise, rather than the other way around. Note also that you assumed that division is defined. That may not have been the case in the original problem.

[–] [email protected] 0 points 3 weeks ago (1 children)

isnt that how methods like proof by contrapositive work ??

[–] [email protected] 0 points 3 weeks ago (1 children)

Proof by contrapositive would be c<0 ∨ c≥1 ⇒ … ⇒ xc≥x. That is not just starting from the conclusion and deriving the premise.

[–] [email protected] 0 points 3 weeks ago (1 children)
[–] [email protected] 0 points 3 weeks ago

Then don’t get involved in this discussion.

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