Calculus & Analysis Marathon & Questions (1 Viewer)

davidgoes4wce

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Re: First Year Uni Calculus Marathon

So as I said, use the "hint" provided in the question to evaluate the sum and then calculating the limit will be fairly straightforward.
Having done further work on it last night, I dont feel like Im getting closer to the answer. Try to used the trig identity to simplify but am coming up with uncancellable terms.



I think from the 2nd line onwards of my working, there are no more limits involved in this question.
 

seanieg89

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Re: First Year Uni Calculus Marathon

Why have you removed the lim? You haven't evaluated any limits, your expression still depends on n.

To evaluate the limit think about what happens to each term and group them accordingly, before making use of basic trig limits such as the high school syllabus result: sin(t)/t -> 1 as t -> 0.
 

davidgoes4wce

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Re: First Year Uni Calculus Marathon

Why have you removed the lim? You haven't evaluated any limits, your expression still depends on n.

To evaluate the limit think about what happens to each term and group them accordingly, before making use of basic trig limits such as the high school syllabus result: sin(t)/t -> 1 as t -> 0.
After reading what you said, my thinking is the sin limit can get reduced to 1?

 

seanieg89

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Re: First Year Uni Calculus Marathon

After reading what you said, my thinking is the sin limit can get reduced to 1?

The limit you have written in this post is not true, the numerator tends to 0 and the denominator is a nonzero constant, so the fraction you have written converges to 0.
 

KingOfActing

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Re: First Year Uni Calculus Marathon



Not sure how to go about that one, thinking Fundamental Theorem of Calculus is involved.
Let the antiderivative of , then use the Fundamental Theorem of Calculus and consider the limit definition of the derivative.
 

dan964

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Re: First Year Uni Calculus Marathon

I think you need to replace your f(x) with F(x), with F'(x) = f(x)= .
Not really he could just set f'(x)= and solve the DE :)
It is just ambiguous.

And yes he can use the FTC, but does he need to check or at least affirm the conditions. f has to be C1? (or if using your notation F)
on the interval of question.
 

seanieg89

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Re: First Year Uni Calculus Marathon

Not really he could just set f'(x)= and solve the DE :)
It is just ambiguous.

And yes he can use the FTC, but does he need to check or at least affirm the conditions. f has to be C1? (or if using your notation F)
on the interval of question.
The FTC applicable in this case (the first FTC according to wikipedia, although nomenclature varies) tells you that if f(t) is a continuous function on [a,b], then



is differentiable in (a,b), with



I.e all you need is that the function f is continuous, which is clearly true from it being a composition of basic functions known to be continuous. That these basic functions are continuous, and that continuity is preserved by composition is the sort of thing you wouldn't bother proving unless it was clear that the question was testing that particular skill. Perhaps worth mentioning in a first year course though.
 

Paradoxica

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Re: First Year Uni Calculus Marathon

Assuming a uniform weighting of the interval [0,1), what is the geometric mean of all the real numbers in [0,1) ?
 

seanieg89

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Re: First Year Uni Calculus Marathon

It is good practice to try to prove (weighted) AM-GM in this setting.

Suppose f,w are non-negative functions on [0,1] that are continuous (or more generally just Riemann-integrable) and suppose that w has integral 1 on this interval.

Prove that:



Try to carefully justify each step of your argument as much as possible.
 
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InteGrand

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Re: First Year Uni Calculus Marathon

It is good practice to try to prove (weighted) AM-GM in this setting.

Suppose f,w are non-negative functions on [0,1] that are continuous (or more generally just Riemann-integrable) and suppose that w has integral 1 on this interval.

Prove that:



Try to carefully justify each step of your argument as much as possible.
Is this inequality basically an application of (continuous version of) Jensen's inequality?
 
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seanieg89

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Re: First Year Uni Calculus Marathon

Is this inequality basically an application of (continuous version of) Jensen's inequality?
Sure, that is one way to do it. (In exactly the same way the discrete weighted Jensen's proves discrete weighted AM-GM). I would expect in such an answer that a student would prove the continuous form of Jensen's though, as the main emphasis of the exercise is the generalisation of discrete inequalities to continuous inequalities rather than the proof of the AM-GM inequality itself.
 

Paradoxica

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Re: First Year Uni Calculus Marathon

It is good practice to try to prove (weighted) AM-GM in this setting.

Suppose f,w are non-negative functions on [0,1] that are continuous (or more generally just Riemann-integrable) and suppose that w has integral 1 on this interval.

Prove that:



Try to carefully justify each step of your argument as much as possible.
what do I need to know
 

seanieg89

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Re: First Year Uni Calculus Marathon

Here's a cool one to think about:

Here is an exercise to exhibit a couple of quirks of high dimensional solids. (Not as directly related to first year calculus courses as most things in this thread, but it is first year level stuff, and it is in the calculus/analysis ballpark.)

a) By generalising MX2 methods of volume calculation, find an expression for the volume of the n-dimensional ball of radius r in terms of the Gamma function



b) How does this quantity behave asymptotically as n->inf? Interpret this as a comparative statement about n-dimensional balls and n-dimensional cubes.

c) What happens to |B(r-d)|/|B(r)| as n-> inf? Here B(r) denotes the n-dimensional ball of radius r, and d < r is fixed. Interpret this result as a statement about the asymptotic concentration of mass in high dimensional balls.

d) Show that the the limiting behaviour in (c) can occur even if d(n) depends on n and monotonically decreases to zero. For which power rates of decay d(n)=n^(-p) will this happen?

e) Repeat c) and d), this time for strips about the equator. That is, what can we say about the limiting behaviour of |{x in B(r): |x_n| < d}|/|B(r)|? What does this say about the asymptotic concentration of mass in high dimensional balls? Can we take d(n)->0 and still have the same behaviour? At what power rate can d tend to zero with us having the same limiting behaviour?
Here is a question related to a basic tool in the analysis I do.



^ Bunch of unanswered questions of varying difficulty.
 

Paradoxica

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Re: First Year Uni Calculus Marathon

It is good practice to try to prove (weighted) AM-GM in this setting.

Suppose f,w are non-negative functions on [0,1] that are continuous (or more generally just Riemann-integrable) and suppose that w has integral 1 on this interval.

Prove that:



Try to carefully justify each step of your argument as much as possible.
When you originally had equality put up I was flummoxed.

Anyway here's a start.

Since logx is concave, the following holds:



is non-increasing on the entire positive real line

but that's as far as I can think, which seems to be a very short range.
 

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