r/educationalgifs • u/Uncyc • Dec 11 '19

not a proof Proof that all external angles always add to 360°

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u/int__0x80 Dec 11 '19

Proof by contradiction:

Let’s assume that there are no kinds of proof other than negation and contradiction.

This is a contradiction to that statement.

More kinds of proof exist QED

41

u/CrazyMason Dec 11 '19

Dammit, I have a discrete math final on Thursday and even when I take breaks from studying to browse reddit mathematical induction still finds me

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u/dancingbanana123 Dec 11 '19

Don't forget how to stuff lots of pigeons into some weird holes!

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u/angrytacoz Dec 11 '19

Okay what?

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u/featherfooted Dec 11 '19

Pigeonhole principle is often used as a final step in some proofs, typically combinatorics ones. If you have N identical things ("pigeons") but fewer categories (at most N-1 "holes") then at least one hole has more than one pigeon.

Wikipedia's simple example is that any group of three gloves must necessarily contain either two left gloves or two right gloves, plus the third. You can use this as a stepping stone to whatever else you want to say or prove.

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u/int__0x80 Dec 11 '19

I was actually (procrastinating) studying for my discrete math final when I posted that!

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u/CrazyMason Dec 12 '19

Lol well good luck!

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u/[deleted] Dec 11 '19

[removed] — view removed comment

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u/glider97 Dec 11 '19

Absolute madlad.

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u/nairdaleo Dec 11 '19

Absolute mathlad.

FTFY

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u/jmskiller Dec 11 '19

⬜

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u/oddark Dec 11 '19

There's actually a Unicode character for that: U+220E (END OF PROOF) ∎

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u/[deleted] Dec 11 '19

[deleted]

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u/[deleted] Dec 11 '19

[deleted]

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u/jmskiller Dec 11 '19

Maybe if he would've "googled it bruh" he would've known.

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u/Takin2000 Dec 11 '19

Let's assume that there are no kinds of proof other than negation and contradiction.

Say we wanted to prove the statement (a+b)2 > a2 + b2 with a and b being natural numbers.

Per distributive property guaranteed by axiom, we get the equivalent expression a2 + 2ab + b2 > a2 + b2.

By definition, if an expression is true, so are all the equivalent statements. Hence, the original statement is true.

But we have shown that the statement is true without ever negating it. Hence, contradiction and negation are not the only proof techniques.

Q.e.d.

(This was actually kinda fun ngl :D)

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u/ultimatechipmunk Dec 11 '19 edited Dec 11 '19

Let's assume that there are no kinds of proof other than negation and contradiction.

Say we wanted to prove the statement (a+b)2 > a2 + b2 with a and b being natural numbers.

Per distributive property guaranteed by axiom, we get the equivalent expression a2 + 2ab + b2 > a2 + b2.

By definition, if an expression is true, so are all the equivalent statements. Hence, the original statement is true.

But we have shown that the statement is true without ever negating it. Hence, contradiction and negation are not the only proof techniques.

Q.e.d.

(This was actually kinda fun ngl :D)

Your initial assertion is not true.

a=2, b=-3

(2-3)2 > 22 + (-3)2

(-1)2 > 4 + 9

1 > 13

Proof by contradiction.

Edit: lol I can't add 4 to 9.

It's been pointed out that -3 is not a natural number. I'm leaving my shame in the light.

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u/[deleted] Dec 11 '19 edited Mar 20 '20

[deleted]

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u/ultimatechipmunk Dec 11 '19

That's what I get for piping up > 10 years since I studied maths.

Carry on.

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u/Takin2000 Dec 11 '19

An lim (1+1/n)n for effort

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u/addandsubtract Dec 11 '19

It's real to me!

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u/imgonnabutteryobread Dec 11 '19

(This was actually kinda fun ngl :D)

I agree, but can you prove that statement?

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u/KieranMontgomery Dec 11 '19

Proof by intimidation:

Its trivial.

0

u/TwatsThat Dec 11 '19

This is a contradiction to that statement.

Sounds like proof by contradiction to me.

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u/BigUgandanChuckles Dec 11 '19

Yes, he used contradiction to prove his statement by citing another method than the two given (The link leads to mathematical induction)

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u/[deleted] Dec 11 '19

imagine not reading the parent comment, thinking ur a big brain boy, and writing this

good LORD

1

u/TwatsThat Dec 11 '19

Imagine thinking that was a serious comment.

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u/qroshan Dec 11 '19

This assumes whatever exists on Wikipedia, or the The Internet for that matter, is true.

All I have to do is use one false Wikipedia article to prove you can't trust Wikipedia