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From: Peter on 14 Nov 2009 08:13
Hi! Please could someone help me? I would like to know how to solve
the subject expression in terms of x and t. I gather the correct
solution is d^2x/dt^2 = 2x/t^2. If this is correct, how do I arrive
to it? Could I present it just at it is?
From: KY on 13 Nov 2009 22:36
http://www.wolframalpha.com/input/?i=+d%5E2x%2Fdt%5E2+%3D+2x%2Ft%5E2.
From: Peter on 14 Nov 2009 10:16
On Nov 14, 8:36 am, KY <wkfkh...(a)yahoo.co.jp> wrote:
> http://www.wolframalpha.com/input/?i=+d%5E2x%2Fdt%5E2+%3D+2x%2Ft%5E2.

Thank you very much. Do you mean that I could put in a paper (which I
am writing) x"(t) = 2x(t)/t^2 without more explanation? Is it
acceptable?
From: Greg Neill on 14 Nov 2009 10:29
Peter wrote:
> On Nov 14, 8:36 am, KY <wkfkh...(a)yahoo.co.jp> wrote:
>> http://www.wolframalpha.com/input/?i=+d%5E2x%2Fdt%5E2+%3D+2x%2Ft%5E2.
>
> Thank you very much. Do you mean that I could put in a paper (which I
> am writing) x"(t) = 2x(t)/t^2 without more explanation? Is it
> acceptable?

No. It is not acceptable. x''(t) = 2x(t)/t^2 only holds
under particular conditions; it is not true in general.


From: Peter on 14 Nov 2009 11:18
On Nov 14, 10:29 am, "Greg Neill" <gneil...(a)MOVEsympatico.ca> wrote:
> Peter wrote:
> > On Nov 14, 8:36 am, KY <wkfkh...(a)yahoo.co.jp> wrote:
> >>http://www.wolframalpha.com/input/?i=+d%5E2x%2Fdt%5E2+%3D+2x%2Ft%5E2.
>
> > Thank you very much. Do you mean that I could put in a paper (which I
> > am writing) x"(t) = 2x(t)/t^2 without more explanation? Is it
> > acceptable?
>
> No.  It is not acceptable.  x''(t) = 2x(t)/t^2 only holds
> under particular conditions; it is not true in general.

I understand it is true when the force is constant. Are there other
conditions?
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