# Let's discuss Mathematics

Discussion in 'Science & Technology' started by ParadigmShifter, Mar 16, 2009.

1. ### monikernemoWarlord

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I thought that you were initially suggesting that having many "uninteresting" object is the flaw of the "true false" logic. Then again being "interesting" is subjective.

2. ### KyriakosAlien spiral maker

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No, I never said they are a flaw (ironically, you can even form this in the P--->Q fashion). How can something that produces stuff be itself responsible for a flaw when it is a mental construction? Mental constructions don't have unintended byproducts like physical constructions do (again from the hypothetical point of view of the construction itself ) and this because in a mental construction the observer (you) is very linked to the construct (your mental world).

Anyway, the first to create a formal logic system was Aristotle, and his included more than true/false (also had "indistinct"). The dynamics of that system were different due to using a larger grammar (basically that of the greek language). But it should be noted that the first to present a formal system where stuff like that in the current one are true, was Philon of Megara, who famously argued that a false conditional will always bring about a true statement.

3. ### KyriakosAlien spiral maker

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A very general question.
What kind (ie relatively more tied to which current) of "future math" do you think Erdos had in mind, when he spoke of those possibly being needed to prove the Collatz Conjecture?

4. ### SamsonDeity

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Linear: y = ax + b
Quadratic: y = ax^2 + bx + c
Cubic: y = ax^3 + bx^2 + cx + d

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Quadratic's root is the same as square. So 4 sides, but literally x^2

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6. ### KyriakosAlien spiral maker

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Here periphrasis is used, and they are called "first degree", "second degree" etc

7. ### KyriakosAlien spiral maker

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I think it is also worth noting that virtually no highschool student is actually aware of why the formulae for third-degree equations work. Even second degree are learned mainly as formulae leading to two roots for real numbers. It would help if students actually relied less on memorizing some formulae, cause no one is going to examine something new by just parroting those.
Then again, what do you expect when almost all of the math "problems" to be solved in exams merely ask you to turn the equation into a difference or addition of squares? You don't need insight on how lego are created, if all you want to do is model the same hut 1000 times.

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I'm not sure how my colleagues do it but I guarantee that I prove all the second degree formulas to my students every year (those who are on the year where they get taught how to solve them of course), showing them how you find the roots (if they exist) and why in other cases they don't.

9. ### KyriakosAlien spiral maker

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Also, it is a gimmick to have a problem which just needs you to memorize the third degree formulaes or you are stuck, when you don't even know why they work. Rewarding isolated memory isn't a good idea, non?

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Third degree isn't really a subject we study (except if there's an obvious root, which means it's just the study of a second degree equation), although sometimes when we start talking about complex numbers it's mentioned that "i" was first invented for third degree equations.

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11. ### KyriakosAlien spiral maker

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Hm, isn't it a bit underwhelming to just ask you if you know what logarithms are and how to do power multiplication?

Maybe it was just 1 out of 5 million questions or something.

12. ### SamsonDeity

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The past oxford admissions exams are all online, the maths ones here. Does not look trivial to me.

13. ### KyriakosAlien spiral maker

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I suppose it is directed to people who just graduated from highschool (?) and it has a large number of questions.
But how is the log base2 of 3 upper/lower bound question not trivial for that age?
I am not saying it should have math olympiad-type questions, just that one question seemed a bit strange

14. ### KyriakosAlien spiral maker

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Maybe this should have been in the Oxford entrance exam

15. ### SamsonDeity

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Is the statement "Covid cases are exponential" the same as saying "R is constant", or more exactly "R and generation interval are constant, or in an inverse relationship"?

An exponential relationship is one such that y = a + b * R ^ x? So would a constant rate of infection be exponential (R = 1)?

Last edited: Nov 13, 2020
16. ### CKSDeity

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In math, yes. Or, "R is approximately constant."
In English, no. In English, "Covid cases are exponential," or "Covid cases are growing exponentially," just means that the number of cases is growing fast. Some people may use exponential correctly in math terms, but not very many people (at least in the USA).
It would be exponential, but we would not say that. Usually we say that something is growing exponentially or falling exponentially, rather than just saying it is exponential, since whether it is growing or falling is kind of important. If it were neither rising or falling, we'd describe it more simply as being constant, even through it can be described as exponential.

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I wouldn't say that it just means "growing fast", more that the speed of the spread is rising as the number of cases rises.

18. ### Lohrenswald老仁森林

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beta=ln(x^2+2ixy-y^2-a^2)+Uix-Uy

anyone know how this can be written in a form like ci+d?

19. ### monikernemoWarlord

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The logarithm part can be refactored to:
ln(x+iy+a)+ln(x+iy-a)

Now suppose that a is fixed, and you take some suitable branch cut for ln (such that x+iy -a, x+iy-a is not in the domain)so ln(x+iy+a)+ln(x+iy-a) is holomorphic for this domain. In particular, if I am not wrong, you can find (real) harmonic functions, A, B such that

A(x,y) +iB(x,y) = ln(x+iy+a) + ln(x+iy-a).

Hope this helps.