Solving a Math Problem. [Physics]

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From: Zurab57 on 5 Apr 2010 10:22

On Apr 5, 12:14 pm, Sanny <softtank...(a)hotmail.com> wrote:
> > >I had left Mathematics 20 years back and I have never read a Math book
> > >for last 20 years So dont accept me to remember all formulas.
>
> > There is no "formula" to remember, but procedures.
> > You do know how to differentiate an expression like
>
> I am satisfied with "Virgil" response. He told it needs L'Hôpital's
> rule.
>
> Actually the girl just asked me to use this equation
>
> nx^n-1=80
>
> So I was confused from where it came. Incase she had told me that she
> used L'Hôpital's rule then I would have understood it quickly.
>
> So I know its just a simple differentiation.
>
> Bye
> Sanny
>
> Ask your Physics Question:http://www.getclub.com/Problems.php?cat=Physics
>
> Or Earn money Solving others Questions.http://www.getclub.com/Problems.php?cat=Physics

Maybe it is not exact case of the girl you told, but to find result is
quite simple. Look:
A^5-B^5=(A-B)(A^4+A^3B+A^2B^2+AB^3+B^4) -
http://www.curiousmath.com/index.php?name=News&file=article&sid=87
So you just have to count:
2^4+2^3X2+2^2X2^2+2X2^3+2^4=16+16+16+16+16=80

From: Sam Wormley on 5 Apr 2010 10:56

On 4/5/10 1:55 AM, Sanny wrote:
> lim (x-> 2) [x^n - 2^n] / [x-2] == 80

http://www.wolframalpha.com/input/?i=lim+x-%3E2++%5Bx%5En+-+2%5En%5D+%2F+%5Bx-2%5D+%3D+80+

From: Ray Vickson on 5 Apr 2010 11:15

On Apr 4, 11:55 pm, Sanny <softtank...(a)hotmail.com> wrote:
> I was boasting about my Physics/ Maths to a small girl appearing for
> IIT [Engineering School]
>
> I solved many Maths/ Physics Problems.
>
> But then she gave me a difficult question. That I could not solve.
>
> She had the answer at back of the booklet. She told me some formula.
> But I was not convinced.
>
> Here is the Question.
>
> lim (x-> 2) [x^n - 2^n] / [x-2] == 80
>
> In the above equation what is the value of "n"
>
> Solve it and tell me?
>
> Bye
> Sanny
>
> Ask your Physics Question:http://www.getclub.com/Problems.php?cat=Physics
>
> Or Earn money Solving others Questions.http://www.getclub.com/Problems.php?cat=Physics

Let x = 2 + r, |r| a small number that goes to zero in the limit. Your
ratio = [(2+r)^n - 2^n]/r; you can use the binomial expansion (2+r)^n
= 2^n + n*2^(n-1)*r + terms in r^2, r^3, ... which holds even if n is
not an integer. Thus, ratio = [n*2^(n-1)*r + ... ]/r = n*2^(n-1) +
terms in r, r^2, ... . As r --> 0 we have n*2^n = 2*80 = 160, hence n
= 5. Of course, all this is equivalent to using l'Hopital's rule.

R.G. Vickson

From: Uncle Al on 5 Apr 2010 12:08

Sanny wrote:
>
> I was boasting about my Physics/ Maths to a small girl appearing for
> IIT [Engineering School]
[snip]

She should have spit in your eye.

> But then she gave me a difficult question. That I could not solve.

Bathe. Many people do it to no apparent detriment.

> She had the answer at back of the booklet. She told me some formula.
> But I was not convinced.
>
> Here is the Question.
>
> lim (x-> 2) [x^n - 2^n] / [x-2] == 80
>
> In the above equation what is the value of "n"
>
> Solve it and tell me?

Big mouth, no brain, SOP...

idiot

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz4.htm

From: Double-A on 5 Apr 2010 14:12

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