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Offlinefuture
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Registered: 12/05/07
Posts: 408
Last seen: 15 years, 6 months
Re: I need a math genius [Re: DieCommie]
    #7951412 - 01/29/08 05:08 PM (16 years, 3 days ago)

Quote:

DieCommie said:
(4x-1)(x+3)/((2x-1)^2)(x+3)(3x+2))




your positive?


--------------------
I am the fakest person on this site. I only pretend to grow and consume illegal mushrooms. I have no knowledge what so ever on any scheduled substance because I know and respect the governing law in the United States of America. All pictures and dialogue posted by me is entirley copyrighted from those who wish to knowingly ignore the laws. I only post these messages as a mere propaganda technique used to gain attention and admiration from others. Thank You


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InvisibleDieCommie


Registered: 12/11/03
Posts: 29,258
Re: I need a math genius [Re: future]
    #7951548 - 01/29/08 05:28 PM (16 years, 3 days ago)

:rolleyes:  no... why dont you check it just to make sure...

You do know the method to factor this right?  And the method to check?  If not I suggest you see your teacher during office hours for help.


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Offlinefuture
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Registered: 12/05/07
Posts: 408
Last seen: 15 years, 6 months
Re: I need a math genius [Re: DieCommie]
    #7951584 - 01/29/08 05:35 PM (16 years, 3 days ago)

the numerator should be different, I checked it.

You were close tho

turns out it's 11x^2 - x - 11 OVER (2x-1) (x+3) (3x+2)


--------------------
I am the fakest person on this site. I only pretend to grow and consume illegal mushrooms. I have no knowledge what so ever on any scheduled substance because I know and respect the governing law in the United States of America. All pictures and dialogue posted by me is entirley copyrighted from those who wish to knowingly ignore the laws. I only post these messages as a mere propaganda technique used to gain attention and admiration from others. Thank You


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OfflineTheCow
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Registered: 10/28/02
Posts: 4,790
Last seen: 15 years, 6 months
Re: I need a math genius [Re: DieCommie]
    #7951588 - 01/29/08 05:35 PM (16 years, 3 days ago)

hey I have a question for you.
suppose { = integral symbol

J(y)={x^4 * (y(x)')^2 dx
where y' is of course the derivative of y

Prove that J cannot have a local minimum in the set
S = y (element of) C2[-1,1] : y(-1)=-1 and y(1)=1
C2 is the vector space of continuous functions with 2 derivatives

Oh and you cant prove it using the euler-lagrange equation


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OfflineTheCow
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Re: I need a math genius [Re: DieCommie]
    #7951591 - 01/29/08 05:36 PM (16 years, 3 days ago)

I have an answer I think is correct, but I was wondering if you have a different take on it that might make more sense


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Offlinefuture
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Registered: 12/05/07
Posts: 408
Last seen: 15 years, 6 months
Re: I need a math genius [Re: TheCow]
    #7951612 - 01/29/08 05:43 PM (16 years, 3 days ago)

the answer is irrational sinc 11x^2 - x - 11 can't be factored.


--------------------
I am the fakest person on this site. I only pretend to grow and consume illegal mushrooms. I have no knowledge what so ever on any scheduled substance because I know and respect the governing law in the United States of America. All pictures and dialogue posted by me is entirley copyrighted from those who wish to knowingly ignore the laws. I only post these messages as a mere propaganda technique used to gain attention and admiration from others. Thank You


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Offlinefuture
Stranger
Registered: 12/05/07
Posts: 408
Last seen: 15 years, 6 months
Re: I need a math genius [Re: TheCow]
    #7951617 - 01/29/08 05:44 PM (16 years, 3 days ago)

Quote:

TheCow said:
I have an answer I think is correct, but I was wondering if you have a different take on it that might make more sense




that stuffs beyond me lol


--------------------
I am the fakest person on this site. I only pretend to grow and consume illegal mushrooms. I have no knowledge what so ever on any scheduled substance because I know and respect the governing law in the United States of America. All pictures and dialogue posted by me is entirley copyrighted from those who wish to knowingly ignore the laws. I only post these messages as a mere propaganda technique used to gain attention and admiration from others. Thank You


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InvisibleDieCommie


Registered: 12/11/03
Posts: 29,258
Re: I need a math genius [Re: TheCow]
    #7951719 - 01/29/08 06:07 PM (16 years, 3 days ago)

Quote:

TheCow said:
hey I have a question for you.
suppose { = integral symbol

J(y)={x^4 * (y(x)')^2 dx
where y' is of course the derivative of y

Prove that J cannot have a local minimum in the set
S = y (element of) C2[-1,1] : y(-1)=-1 and y(1)=1
C2 is the vector space of continuous functions with 2 derivatives

Oh and you cant prove it using the euler-lagrange equation




Ha, you think I can understand your graduate level shit?  You are way beyond me in skills.  Is this for your calculus of variations class? 

I honestly have had a real hard time in post-calculus/diff. eq. maths.  Proof writing, as well as all that orthogonal function stuff is very difficult for me. 

From freshman calculus to find a local min, you do the first and second derivative tests.  I tried something like that for this but it was an epic fail.  :sith:


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OfflineTheCow
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Registered: 10/28/02
Posts: 4,790
Last seen: 15 years, 6 months
Re: I need a math genius [Re: DieCommie]
    #7951730 - 01/29/08 06:10 PM (16 years, 3 days ago)

Yea its for variational calculus. But I'm supposed to solve it without using variational calculus. So I thought you might have an insight if you'd taken any upper division math classes that have proofs and whatnot. I'm pretty bad at proofs also, and don't know nearly enough pure math. Not sure why I'm taking a class offered by the math department, horrible idea in hindsight


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Offlinefuture
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Registered: 12/05/07
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Last seen: 15 years, 6 months
Re: I need a math genius [Re: TheCow]
    #7951741 - 01/29/08 06:13 PM (16 years, 3 days ago)

welcome to college :rolleyes:


--------------------
I am the fakest person on this site. I only pretend to grow and consume illegal mushrooms. I have no knowledge what so ever on any scheduled substance because I know and respect the governing law in the United States of America. All pictures and dialogue posted by me is entirley copyrighted from those who wish to knowingly ignore the laws. I only post these messages as a mere propaganda technique used to gain attention and admiration from others. Thank You


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Offlinetrepanib
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Male

Registered: 02/16/07
Posts: 648
Loc: Boston, MA/ Syracuse, NY
Last seen: 13 years, 6 months
Re: I need a math genius [Re: future]
    #7951931 - 01/29/08 06:43 PM (16 years, 3 days ago)

The cow's shit is way more difficult than yours.

BTW Cartesian coordinates suck. Polar coordinates rock!!!!


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InvisibleFerris
PsychedelicJourneyman
Male

Folding@home Statistics
Registered: 03/12/06
Posts: 11,529
Re: I need a math genius [Re: trepanib]
    #7951947 - 01/29/08 06:45 PM (16 years, 3 days ago)

Quote:

trepanib said:
BTW Cartesian coordinates suck. Polar coordinates rock!!!!




Only if you're doing 3 dimensional vectors ya godamn elitist :smirk:


--------------------

Discuss Politics


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InvisibleDieCommie


Registered: 12/11/03
Posts: 29,258
Re: I need a math genius [Re: trepanib]
    #7952050 - 01/29/08 07:02 PM (16 years, 3 days ago)

Quote:

trepanib said:
The cow's shit is way more difficult than yours.

BTW Cartesian coordinates suck. Polar coordinates rock!!!!


  Cylindrical or spherical?

How about Oblate spheroidal coordinate system?  I dont know when I would want to use it, but I had to construct it for a project last semester.  :nerd:


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OfflineKarmatron
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Registered: 06/11/06
Posts: 127
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Re: I need a math genius [Re: TheCow]
    #7952143 - 01/29/08 07:22 PM (16 years, 3 days ago)

Quote:

TheCow said:
hey I have a question for you.
suppose { = integral symbol

J(y)={x^4 * (y(x)')^2 dx
where y' is of course the derivative of y

Prove that J cannot have a local minimum in the set
S = y (element of) C2[-1,1] : y(-1)=-1 and y(1)=1
C2 is the vector space of continuous functions with 2 derivatives

Oh and you cant prove it using the euler-lagrange equation




First guess: use the Cauchy-Reimann equations taking the partial derivatives of J(y), show they're nonzero on the interval... you're done? May have to take the total derivative of J first and then manipulate into a convenient expression, too lazy to check that.

Oh, I guess you would also have to exclude the edges from being "local minima" either by checking them or just stating that you exclude them, but your interval is closed so that might not be valid...


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OfflineTheCow
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Registered: 10/28/02
Posts: 4,790
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Re: I need a math genius [Re: Karmatron]
    #7952175 - 01/29/08 07:29 PM (16 years, 3 days ago)

Why would the Cauchy equations apply here? I only remember that from complex analysis. Well basically my proof goes sort of as follows. I can show that to be a minimum y' would have to equal 0, therefore y is a constant. This violates the boundary conditions, so the only possibility would be a piecewise function. However since the initial boundary condition is negative, and the ending is positive that means there was a jump somewhere on the interval. This means that the function is not a C2 function. However looking over my proof, I dont quite remember how I found that y has to be a constant, and my scribble notes where I first derived this are hard to read.


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OfflineKarmatron
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Re: I need a math genius [Re: TheCow]
    #7952325 - 01/29/08 07:52 PM (16 years, 3 days ago)

Well, if y(x) were a constant over the interval, then y'(x) would be zero, making the entire integral zero over the interval, correct?

Cauchy Riemann would apply to real valued functions since it applies to complex, you just get the "real valued" parts only(the "u functions, none of the "v" functions if you know what i mean). It basically means that Laplace's eq's are satisfied over the interval, which may not be valid... I'm used to them being valid because they always are in physics...


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OfflineTheCow
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Re: I need a math genius [Re: Karmatron]
    #7952380 - 01/29/08 08:00 PM (16 years, 3 days ago)

Yes the integral would be zero, that is how im deriving that y' is 0. Basically I have J(y) and J(y_hat) where y_hat=y + epsilon*n where n is some function on C2. Assume J(y) is the minimum and J(y_hat) is the minimum except you added a small amount as is shown above. If I take the taylor expansion of J(y_hat) and subtract it from J(y) I end up with an integral plus O(epsilon^2) i.e I only expanded it out to first derivatives. Therefore we want the difference to equal 0 which would mean that the integral of n*df/dy' should be 0. To do this y' would be 0. Therefore y is a constant.

I doubt thats readable at all, but its hard to explain this on a forum. I still dont see what you mean with Laplaces equation or the Cauchy equations. Ive used both, however I dont see how itd be applied here really. Can you explain what you mean more?


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Offlineg00ru
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Registered: 08/09/07
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Re: I need a math genius [Re: Karmatron]
    #7952385 - 01/29/08 08:00 PM (16 years, 3 days ago)

I don't know much about math, everything I've retained comes from making bitchin graph art on my TI-82.

Every time I learned a new concept in calc or trig I would get excited because now my art would have exciting new dimensions.


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OfflineKarmatron
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Registered: 06/11/06
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Re: I need a math genius [Re: Karmatron]
    #7952388 - 01/29/08 08:01 PM (16 years, 3 days ago)

But doesn't J(y) have to be zero in both the x and y axes for it to have a max/min/saddle? That's my motivation for using Cauchy/Laplace. Then you could use the boundaries to calc the integral directly at the edges.


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OfflineTheCow
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Re: I need a math genius [Re: TheCow]
    #7952398 - 01/29/08 08:02 PM (16 years, 3 days ago)

Since I have limits x1, and x2 however it seems that y' could be something other then 0. For instance it seems like itd be possible to have a function other then 0 that when the limits are applied the integral would equal 0.


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