## Search found 221 matches

Fri Apr 27, 2012 7:14 am UTC
Forum: Mathematics
Topic: A curious connection
Replies: 5
Views: 2188

### Re: A curious connection

Holy "five years late" batman!
Sun Apr 22, 2012 6:23 am UTC
Forum: Mathematics
Topic: Odd/stupid/interesting question
Replies: 4
Views: 1356

### Re: Odd/stupid/interesting question

Time to search through that old collection of (functions with) negative definite hessian's for some global maxes.
Sun Apr 22, 2012 6:15 am UTC
Forum: Mathematics
Topic: A sequence of adding the product of their prime factors
Replies: 5
Views: 1567

### Re: A sequence of adding the product of their prime factors

Meteoric wrote: But that doesn't at all match the sequence you gave, so at least one of us is misunderstanding something.

The op's sequence is listing where the number 1 goes, then where 2, goes, then where 3 goes.... so, for example, the 12th number in their list (since 12=2*2*3) is 2+2+3=7.
Sun Apr 22, 2012 6:12 am UTC
Forum: Mathematics
Topic: A sequence of adding the product of their prime factors
Replies: 5
Views: 1567

### Re: A sequence of adding the product of their prime factors

The "sum of prime factors" fucntion or sopfr is defined here. http://mathworld.wolfram.com/SumofPrimeFactors.html you want to look at the fourth paragrph where they iterate to a fixed point. The only difference between yours and theirs is that their sum of the factors of one (other than on...
Fri Apr 20, 2012 2:16 am UTC
Forum: Mathematics
Topic: Need advice on bizarre accidental problem
Replies: 13
Views: 3295

### Re: Need advice on bizarre accidental problem

If you're worried that you lucked into passing the test trying taking it again, or take a different but similar test. This http://www.math.unt.edu/mathlab/emathlab/review%20test%20%28college%20algebra%29.htm was the first google hit when I went looking for an additional test for you. Try it. See if ...
Sun Feb 19, 2012 4:21 am UTC
Forum: Mathematics
Topic: A Most Amazing Number
Replies: 33
Views: 17320

### Re: A Most Amazing Number

How so? Do you contend that 1.000… and −1.000… are identical decimal representations? They clearly differ at the ‘sign’ position of the representation, and that is exactly the same representational difference as distinguishes 0.000… from −0.000… I think that they are identical decimal representatio...
Sun Jan 08, 2012 7:11 pm UTC
Forum: Mathematics
Topic: What's the point of rationalizing?
Replies: 61
Views: 9317

### Re: What's the point of rationalizing?

I think I didn't ask my question well enough. I don't see a point in using a calculator either, because the calculator can't give me a finished answer for \sqrt3 either. Sometimes one is interested in whether or not \sqrt3-1.73 is positive or negative, for instance if it is under a radical and we k...
Sat Dec 17, 2011 8:36 am UTC
Forum: Mathematics
Topic: Introduction to Linear Algebra Exam Soon - Need Help
Replies: 8
Views: 5402

### Re: Introduction to Linear Algebra Exam Soon - Need Help

Myson is starting at introduction to algebra 1 his freshman year in high school will he be behind in math? I want to know should he be starting at Algebra 1 and not at Introduction to algebra 1 .Will this efefect him in the next years making him behind. You should probably start a new thread with t...
Thu Dec 15, 2011 12:13 am UTC
Forum: Mathematics
Topic: What pre-calculus needed for this calculus class?
Replies: 2
Views: 981

### Re: What pre-calculus needed for this calculus class?

Often times classes like those avoid trig functions. So I would say to put most of your study effort towards chapter 2,3 and 4. And then possibly review a bit of the vector material from chapter 7.
Mon Nov 28, 2011 2:53 am UTC
Forum: Mathematics
Topic: Elementary Real Analysis Proof Validity
Replies: 8
Views: 1865

### Re: Elementary Real Analysis Proof Validity

You can still use your differentiability argument without assuming the function is differentiable. All you need to do is show that it's differentiable... You essentially have already shown that f was differentiable at x when you showed that the limit of the absolute value of the quotient was 0. So t...
Wed Nov 16, 2011 7:15 am UTC
Forum: Mathematics
Topic: Help Me Understand?
Replies: 6
Views: 1510

### Re: Help Me Understand?

I'm not sure I agree with this: If for every unique apple there's a unique orange then there are as many or more oranges as apples. It's works for integers I guess... but does that mean it automatically should work for everything else? How would you prove something like this? I'm not very smart and...
Wed Nov 16, 2011 7:03 am UTC
Forum: Mathematics
Topic: Help Me Understand?
Replies: 6
Views: 1510

### Re: Help Me Understand?

Isn't this a counter example?: Say the numbers on apples {1, 1, 2}, and on oranges {1, 2} (each number representing the number written on the fruit). There are two unique apples and two unique oranges, but there are more apples than oranges I think you actually have three unique apples there. 2 of ...
Wed Oct 19, 2011 1:06 am UTC
Forum: Mathematics
Topic: A Semantic Survey
Replies: 17
Views: 2358

### Re: A Semantic Survey

Situation: Three cards are drawn from a standard deck. Statement: All three are not hearts. Trial: 3 of Hears, King of Hearts, 4 of Spades. Question: The trial outcome satisfies the statement. True or False? Three cards are drawn, so I read "All three" as "all of the drawn cards"...
Sun Oct 16, 2011 7:28 am UTC
Forum: Mathematics
Replies: 53
Views: 9602

### Re: Post your interesting/challenging/fun integrals

Here's one that I stumped my high school class with for a few days: \int \frac{1}{x \log x} \,dx Try solving it through integration by parts ( u = \frac{1}{\log x}, dv = \frac{1}{x} \,dx ) I assume that the u has to be a v or the dv has to be an u. The way I get to the answer: \int \frac{1}{x \log ...
Sun Oct 09, 2011 2:19 am UTC
Forum: Mathematics
Topic: Is it possible to aperiodically tile a sphere?
Replies: 31
Views: 15053

### Re: Is it possible to aperiodically tile a sphere?

I wanted to make one, however after contacting the author and talking to people here I found out it wasn't real. I still want to make something similar, but something that is real. (Please insert your own idea of what is 'real') You can cheat. The sphere will undoubtedly be either hanging or sittin...
Sat Oct 08, 2011 3:06 am UTC
Forum: Mathematics
Topic: 0^-1
Replies: 20
Views: 3091

### Re: 0^-1

What I thought of it is 0 -1 =1/0 1 =infinity? but x^{-1}= \frac{1}{x} only for non-zero x. So assuming that 0^{-1} "should" equal 1/0 is the "wrong" decision (since we long ago decided that dividing by zero is a poor choice). In the case of 0^{-1} I think a case can be made tha...
Sat Oct 08, 2011 1:58 am UTC
Forum: Mathematics
Replies: 46
Views: 14627

### Re: Your favorite "tricky" integrals?

Do any of you have favorite "tricky" integrals? Something like \int \frac{1}{1+\sin(x)}\,dx is nice. Especially if you don't cover the Weierstrass substitution in class. Less tricky, but ones that I've always enjoyed are the ones where you "get back the original integral"...
Fri Oct 07, 2011 5:04 am UTC
Forum: Mathematics
Topic: Who invented Infinity=infinity+1?
Replies: 24
Views: 5171

### Re: Who invented Infinity=infinity+1?

Qaanol wrote:
lalop wrote:Why is everyone here talking as if infinity was a number?

Because infinity and 5 are effectively indistinguishable.

And here I always thought it was infinity and 8 that were hard to tell apart.
Thu Oct 06, 2011 5:46 am UTC
Forum: Mathematics
Topic: Should we make students memorize the quadratic formula?
Replies: 61
Views: 8944

### Re: Should we make students memorize the quadratic formula?

I had to look up 'FOIL' ... you guys are really taught that as an acronym? I found we stopped with those after BODMAS in grade 6, and from then on we were told to use the distributive law (although we didn't call it that for some obscure reason). And I had to look up BODMAS :) Which it appears is j...
Mon Oct 03, 2011 5:57 am UTC
Forum: Mathematics
Topic: Should we make students memorize the quadratic formula?
Replies: 61
Views: 8944

### Re: Should we make students memorize the quadratic formula?

I can finely have my own opinion we should defiantly not give it to them Either you are making a very subtle point, or one of us needs to spend more time memorizing vocab words. Oh the later for sure. I'm "definitely" as bad at memorizing vocab as my students are at memorizing the quadrat...
Mon Oct 03, 2011 4:18 am UTC
Forum: Mathematics
Topic: Should we make students memorize the quadratic formula?
Replies: 61
Views: 8944

### Re: Should we make students memorize the quadratic formula?

With the exception of the last one, I actually feel like those should be fair game. I actually agree with you too. I was just going to a bit of an absurdest level with a number of things we are asked to memorize (or partially memorize-- I hope no one had to memorize moby dick.) in school. My little...
Mon Oct 03, 2011 2:41 am UTC
Forum: Mathematics
Topic: Should we make students memorize the quadratic formula?
Replies: 61
Views: 8944

### Re: Should we make students memorize the quadratic formula?

I think it's a bit much to make students memorize it. A bit much!?! It's in the neighborhood of 20 words if you speak it. I remember being asked to memorize mush much longer things in my Middle school and High school English classes, History classes, Biology... Heck I even had to memorize rules for...
Thu Sep 22, 2011 5:40 am UTC
Forum: Mathematics
Topic: Why standard deviation?
Replies: 24
Views: 4797

### Re: Why standard deviation?

Are you wondering why we don't just use the variance instead of taking its square root? Or are you wondering why we care about such things at all? Or is this a question of why we like this measure of the "spread" or "dispersion" of the data as opposed to some other way of measuri...
Fri Sep 16, 2011 1:52 am UTC
Forum: Mathematics
Topic: Solve 2^x = x^2 without using "By Observation"
Replies: 21
Views: 34935

### Re: Solve 2^x = x^2 without using "By Observation"

jestingrabbit wrote:... but its exactly the "by observation" that you're being told not to use by the thread title.

No no no. They are using "Fairly obvious" we just need to avoid "by observation" So I think this one stands.
Sat Sep 10, 2011 5:54 am UTC
Forum: Mathematics
Topic: Multiplication or the summation operator (sigma)
Replies: 28
Views: 4456

### Re: Multiplication or the summation operator (sigma)

So is making polls discouraged here or something? This poll, and the lines and curves one, seems almost troll-y to me though. You give very little context on what exactly you are wanting people to compare about two topics both of which are fundamental and (one could argue) indispensable. New Poll! ...
Sun Sep 04, 2011 1:01 am UTC
Forum: Mathematics
Topic: Multiplication or the summation operator (sigma)
Replies: 28
Views: 4456

### Re: Multiplication or the summation operator (sigma)

scratch123 wrote:Idea requests for my next topic are welcome.

How about "Ridiculous poll" or "Pointless poll" you can then use those results for the poll after that.
Thu Aug 18, 2011 5:25 am UTC
Forum: Mathematics
Topic: Order of Operations
Replies: 12
Views: 2312

### Re: Order of Operations

when really he has a legitimate question which is about what he feels is meaningless convention. In some sense it kinda is just a meaningless convention.... But we need some convention so that we can communicate our thoughts with each other. Whether or not the accepted order of operations is the &q...
Thu Aug 18, 2011 5:02 am UTC
Forum: Mathematics
Topic: Practical applications of maths in everyday life?
Replies: 8
Views: 3616

### Re: Practical applications of maths in everyday life?

For people not involved directly with the sciences you typically won't find lot's of direct application. Similar to how most people don't get to directly apply what they learned about the roman empire, or about gerunds, or chord progression, or about the conjugation of french verbs -- Yet as you say...
Tue Aug 09, 2011 12:53 am UTC
Forum: Mathematics
Replies: 7
Views: 1431

Example: Solve for x (exact answer). x = √(2) + √(3) By using the General Addition Formula: x = √(5 + 2√(6)) Your 5 should be a 13, since 2^2+3^2=13 . My intuition tells me that the only time your \sqrt{x}+\sqrt{y}=\sqrt{x^2+y^2+2\sqrt{xy}} formula would be "useful" would be if the inner ...
Tue Jun 21, 2011 6:23 am UTC
Forum: Mathematics
Topic: Repeating decimals represented as fractions
Replies: 11
Views: 2971

### Re: Repeating decimals represented as fractions

Adam Preston wrote:I hope i got this technique correct as I needed to use it in my maths exam.

The example you did looks good. I hope you did well (or will do well) on the exam! Good luck!
Tue Jun 21, 2011 6:20 am UTC
Forum: Mathematics
Topic: Is Khan Academy enough? Trig for Calculus
Replies: 3
Views: 1934

### Re: Is Khan Academy enough? Trig for Calculus

In my opinion what you need trig-wise for calculus is to be familiar enough with it that when you see it you don't freak out and think it's hard. When you see it you need to think "Oh right trig stuff. I can do that." That being said the other things you should "know" are: What t...
Thu Jun 16, 2011 5:52 am UTC
Forum: Mathematics
Topic: Simple math problem
Replies: 7
Views: 1719

### Re: Simple math problem

letterX wrote:But when I put it in my calculator exactly like that, it says 0!!!

Time to get a better calculator or learn how to use the one you have.
Sun May 22, 2011 2:47 am UTC
Forum: Mathematics
Topic: alternative mathematics
Replies: 128
Views: 15274

### Re: alternative mathematics

[b]Natural axiom: Natural along. .... Two questions to start with.... is "Natural" a verb,noun, adjective,...etc? I can't tell if that word is telling us to do something, or if it's telling us something that we do something to, or... and then "along" what? or is along another ne...
Fri Apr 22, 2011 3:39 pm UTC
Forum: Mathematics
Topic: Question about Definitions of Limits Involving Infinity
Replies: 5
Views: 1151

### Re: Question about Definitions of Limits Involving Infinity

Something to think about... What happens when the limiting behavior (as x\to\infty ) of a function is already being realized (that is for some small \varepsilon we have |f(x)-L|<\varepsilon ) for negative (or really any "small" ) x -values? If we can keep our function arbitrarily c...
Mon Apr 18, 2011 6:22 am UTC
Forum: Mathematics
Topic: Guess numbers by knowing their sum and product
Replies: 11
Views: 1870

### Re: Guess numbers by knowing their sum and product

It should be mentioned somewhere in this thread that for N=1 and N=2 the information given is enough to uniquely determine the numbers. If your willing to ask additional questions you can pick up the N=3 case by also asking for the sum (or product) of any two of the numbers. This allows you to easil...
Thu Apr 14, 2011 5:24 am UTC
Forum: Mathematics
Topic: Substitution
Replies: 18
Views: 2701

### Re: Substitution

That does sound like a wonderful idea!
Wed Apr 13, 2011 6:01 am UTC
Forum: Mathematics
Topic: Random Integer
Replies: 18
Views: 2771

### Re: Random Integer

... I think the second could will have labeled the planet with life on it with some infinite number and somewhere in the universe there is a first and last planet... even if there are an infinite number of them. It's similar to, say, how there are an infinite number of reals between 0 and 1 and yet...
Thu Apr 07, 2011 2:53 am UTC
Forum: Mathematics
Topic: What will I be expected to know?
Replies: 3
Views: 984

### Re: What will I be expected to know?

I don't know what you'll be expected to know, but I think it's important for you to be confident with basic algebraic manipulations, like putting things over a common denominator, using the distributive law, solving quadratics, etc. Also, it would be good to be familiar with the exponential and log...
Wed Mar 16, 2011 5:51 am UTC
Forum: Mathematics
Topic: Matrix multiplication seems so arbitrary
Replies: 19
Views: 4577

### Re: Matrix multiplication seems so arbitrary

Why not do something simpler like multiply the columns with each other instead or not add a bunch of numbers together? Also why are there no other ways to multiply 2 sets of numbers together? Others have addressed in depth why our usual matrix multiplication is defined the way it is. They all boil ...
Sun Feb 20, 2011 7:18 am UTC
Forum: Mathematics
Topic: How is l'hopital useful here?
Replies: 15
Views: 2202

### Re: How is l'hopital useful here?

f(x) = \left \{ \begin{array}{lrr} e^{\frac{-1}{x^2}} & for & x \ne 0\\ 0 & for & x=0 \end{array} \right. (Latex questions: Is there a better way to avoid having "for x" run together other than giving "for" it's own column? Can I make the exponent of e lo...