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#76 Re: Help Me ! » solving definite integrals, solving systems uisng Gaussian elimination » 2006-10-11 02:53:02

For the second one, I used row reduction to get this far:

2  0  -14   |  -14
0  1    2    |  4
0  0   22   |  2

And from this I get:



Which checks when substituted back into the system.

#77 Re: Help Me ! » Speaking math » 2006-10-10 15:03:35

For maximum reliability:

1. z is equal to x to the power of open bracket y plus open bracket 2 divided by x close bracket close bracket. big_smile

Actual attempt:

1. z is equal to x raised to the sum of twice the inverse of x and y.

2. z is equal to x raised to the quotient of y + 2 and x.

3. z is equal to twice the inverse of x, plus the yth power of x.

#78 Re: Help Me ! » Problem Solving » 2006-10-10 12:09:35

Eniara wrote:

Of the 56 signers of the declartion of independence, only William Ellery was a lawyer & a merchant.  of the rest, 39 were either lawyers or merchants. there we 9 more lawyers than merchants.  The product of the numbers of these careers is 360.  How many lawyers were there?

let L and M be natural numbers.

L := number of lawyers
M := number of merchants

The relevant data given is: 

L = M + 9  ... (1)

LM = 360   ... (2)

Substitute (9 + M) for L in the second equation:

M^2 + 9M = 360
M^2 + 9M - 360 = 0

Apply the quadratic formula:

M = (-9 +/- 39) / 2

  = 15 or -24

reject -24 since the solution needs natural numbers.

Therefore M = 15

From equation 1:

L = 15 + 9 = 24

So:

There were 15 merchants and 24 lawyers.

Check: 15 + 24 = 39, as stated.

#79 Re: Help Me ! » hmmm a mathamatical problem which has something to do with !! » 2006-10-10 12:03:21

mathsyperson wrote:

I think it's the other way around. x^y^z = x^(y^z), unless otherwise bracketed.

If people wanted to write (x^y)^z, they could just as easily write x^yz.

Hmm, right! So i'm confused again.

Using the idea of evaluating the most deeply nested function first, if we for example in the case of the function i mentioned write:

Then the x^2 must be evaluated first because it then is an argument to the exponential function!

#80 Re: Help Me ! » hmmm a mathamatical problem which has something to do with !! » 2006-10-10 11:55:04

I guess I see now my confusion came from the "bell curve" function

which is not equal to:

because of the negation.  smile

#81 Re: Help Me ! » hmmm a mathamatical problem which has something to do with !! » 2006-10-10 11:20:08

luca-deltodesco wrote:

with no brackets around exponentials, you go in order of bottom to top

so

Thanks. I'm not sure why I was thinking it is actually the other way around.. for example when evaluating:

It might seem natural to square the x first, but then the curve would be all wrong!

#82 Re: Help Me ! » hmmm a mathamatical problem which has something to do with !! » 2006-10-10 07:28:31

I wonder if any of you know for certain.. what is the correct order of multiple nested exponentiation:

For example luca wrote:

In this case the order does not matter:

Because of the funny property x^y = xy  for x = 2, y = 2.

However, for a number like:

We can interpret this as either either:

Or:


(number too large for windows calculator)

So which one is meant when no parentheses are used ?

#83 Re: Help Me ! » matchstick puzzle HELP » 2006-10-10 02:52:45

mahmoudaljamel wrote:

If we move one of the sticks from the group of 3(III) and place it with the single stick (I):

II + II + II = IIII

we have 6 sticks on the left side , while we have 4 sticks on the other 

So ..
polylog solution is wrong

Right, oops. roll

So it doesn't look like there is a way to do this by doing nothing but moving only 1 stick on only the left side, unless we are allowed to replace it with an operator or using it to cross out the equals sign or something.

#85 Re: Help Me ! » A integral problem~~ » 2006-10-10 02:40:15

He means the sinc function sinc(x).

http://mathworld.wolfram.com/SincFunction.html

#86 Re: Help Me ! » matchstick puzzle HELP » 2006-10-09 14:20:45

I think, if I understand this correctly, that '1' here is not a digit, nor these actual numbers.. I think it's supposed to just represent a quantity of sticks. Using '|' instead of '1':

| + || + ||| = ||||

Let's move one of the sticks from the group of 3 (|||) and place it with the single stick (|) :

|| + || = ||||

Now we have four sticks on both sides, which is true. (2 + 2 = 4)

I don't see any other way this could make sense. smile

#87 Re: Help Me ! » Can I derive a hyperbolic formula using 2 points and an asymptote? » 2006-10-09 11:23:59

t is the independent variable, which would be time in this case, on the horizontal axis.

e is the base of the natural logarithm, and is equal to about 2.718281828

e^t is just the standard exponential function that is used to model all kinds of exponential growth in science.


here is an example of such a curve (the top one in this picture):

http://cognitrn.psych.indiana.edu/busey/WWWPubs/PsychRev/Image2.gif

k, which I called a rate constant, is a number that determines how sharply the curve rises at the beginning.

If k = 100 for example, it will rise very sharply, if k = 1, the rise is moderate.

I would suggest plotting a few of these with graph plotting software, like Winplot (which is free and easy to use).

#88 Re: This is Cool » Navier-Stokes (A Millenium Problem) Solved? » 2006-10-09 10:19:00

The author has withdrawn the solution !! sad

http://motls.blogspot.com/2006/10/immortal-smooth-solution-withdrawn.html

#90 Re: This is Cool » Navier-Stokes (A Millenium Problem) Solved? » 2006-10-07 12:56:04

Ok reading the problem stament it seems that is what the prize requires! Awesome. smile

However, its a bit confusing, as it seems the equation is not actually solved -- it's a proof of the existence of smooth solutions -- does this actually help in practical applications?

#91 Re: This is Cool » Navier-Stokes (A Millenium Problem) Solved? » 2006-10-07 12:45:53

It seems like the paper proves the *existence of a solution*, more specifically the existence of an 'immortal smooth solution' (whatever that is)... is this enough for the prize?

#92 Re: Help Me ! » simplify » 2006-10-07 10:25:13

Thanks, I was worried that maybe because the coefficients are perfect squares, there is some clever difference-of-squares-like factorization possible. smile

#93 Re: Help Me ! » Factoring » 2006-10-07 10:23:19

Well I think that's all you can do. By taking out the common factor 2x^(3n + 2), you get:

I think it's a little difficult to see how to get 3x^(n-1) just like that, so perhaps its easier to do it this way:

Now here is the tricky part: if we factor the other 2x, we need to take out an x in the 3x^n term.

We do that by writing:

Because x multiplied by 3x^(n - 1) gives us the original 3x^n.

#95 Re: Help Me ! » simplify » 2006-10-07 09:29:23

If you mean:

Then what you need to do is expand it out and use the laws of exponents:

It might be possible to simplify this more but I can't think of how at the moment. smile

#96 Re: Help Me ! » Partial Fractions » 2006-10-06 12:20:44

For your example, using polynomial long division:

This can be written as:

And I don't think it can be made any simpler.

#97 Re: Help Me ! » Partial Fractions » 2006-10-06 10:35:30

I would suggest carrying out polynomial long division, and then what you obtain from that would be a proper fraction plus another term.

Then the proper fraction has known cases of partial fraction decomposition, which is all straighforward.

#98 Re: Help Me ! » LaTeX - A Crash Course » 2006-10-06 07:50:48

Ok that makes sense, thanks. smile

#99 Re: Help Me ! » Can I derive a hyperbolic formula using 2 points and an asymptote? » 2006-10-06 07:30:17

As John said, an exponential approaching 100% might work nicely.

It has an asymptote at y = 1.

Such a curve would be:

Where k would be a rate constant.

#100 Re: Help Me ! » multiplying and dividing fractions » 2006-10-06 04:02:04

Just for completeness I typed up the solution to (b) as well.

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