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Mathematics 9 Online
OpenStudy (anonymous):

Question on calculus

OpenStudy (anonymous):

\[\prod_{0}^{n}e ^{r/n})]^{1/n}\]

OpenStudy (anonymous):

find the value

OpenStudy (anonymous):

PI e^(r/n^2) correct

OpenStudy (anonymous):

where PI is multiplication i assume

OpenStudy (anonymous):

you want the limit as n goes to infinity

OpenStudy (anonymous):

yes....

OpenStudy (anonymous):

also its not defined for n = 0

OpenStudy (anonymous):

that should be from 1 to n ?

OpenStudy (anonymous):

wait, you probably meant sum, not PRODUCT

OpenStudy (anonymous):

the limit is for r the iteration is r from 0 to n, n tends to inf

OpenStudy (anonymous):

it is defined for r=0

OpenStudy (anonymous):

then your question is ambiguous. theres something wrong with it

OpenStudy (anonymous):

and it is product

OpenStudy (anonymous):

youre messing up your indices

OpenStudy (anonymous):

it says the answer is e^(1/2)

OpenStudy (anonymous):

is this online, can i see it

OpenStudy (anonymous):

can you draw it exactly as it appears

OpenStudy (anonymous):

no we dont work online in india

OpenStudy (anonymous):

here http://www.twiddla.com/543856

OpenStudy (anonymous):

please click on that, and draw the mother trucking expression

OpenStudy (anonymous):

im in usa , here we do everything online.

OpenStudy (anonymous):

oh wait..i got it..thnx neway

OpenStudy (anonymous):

wait, can you show me the expression

OpenStudy (anonymous):

here http://www.twiddla.com/543856

OpenStudy (anonymous):

you can draw the expression there

OpenStudy (anonymous):

\[\lim_{n \rightarrow \infty}[(\prod_{r=0}^{n} (e ^{r/n})]^{1/n}\]

OpenStudy (anonymous):

ohhh

OpenStudy (anonymous):

i got it neway..thnx

OpenStudy (anonymous):

how did you get solution

OpenStudy (watchmath):

e^(1/2)

OpenStudy (anonymous):

ok change the exponent product to sum of exponents

OpenStudy (anonymous):

yes....take log on both sides..it becomes integral (xdx) from 0 to 1

OpenStudy (anonymous):

then exponentiate on both sides

OpenStudy (anonymous):

replace 1/n by dx r/n by x this will give you an integral......note this is one of the derivations of the basic integral ....check out reimannian sums

OpenStudy (anonymous):

lim [ e^0/n *e^(1/n) *e^(2/n)*...e^(n/n)] ^(1/n)

OpenStudy (anonymous):

oh integral e^(1/x) dx ?

OpenStudy (anonymous):

no man

OpenStudy (anonymous):

right, e^x

OpenStudy (anonymous):

ln (e^x)

OpenStudy (anonymous):

theres a direct approach though that works

OpenStudy (watchmath):

cantorset, your expression is simpliefied to \(e^{n(n+1)/(2n^2)}\)

OpenStudy (anonymous):

right

OpenStudy (anonymous):

and then you can take limits directly

OpenStudy (anonymous):

something to that effect note you will still have to take a log first

OpenStudy (anonymous):

if you take the limit as n goes to infinity, you get e^(1/2)

OpenStudy (anonymous):

yes....thanks a lot guys

OpenStudy (anonymous):

lim n> oo [ e^0/n *e^(1/n) *e^(2/n)*...e^(n/n)] ^(1/n)= lim [ e^ (1/n + 2/n + 3/n + ... n/n) ] *1/n

OpenStudy (anonymous):

lim n> oo [ e^0/n *e^(1/n) *e^(2/n)*...e^(n/n)] ^(1/n)= lim [ e^ (1/n + 2/n + 3/n + ... n/n) ] *1/n = lim e^ [( 1 + 2 + 3 + ... + n ) / n ] ^(1/n)

OpenStudy (anonymous):

lim n> oo [ e^0/n *e^(1/n) *e^(2/n)*...e^(n/n)] ^(1/n)= lim [ e^ (1/n + 2/n + 3/n + ... n/n) ] *1/n = lim e^ [( 1 + 2 + 3 + ... + n ) / n ] ^(1/n) =lim e^ (n^2 + n ) / (2n^2)

OpenStudy (anonymous):

you get \[\log (I) = \int\limits_{0}^{1}xdx\]

OpenStudy (anonymous):

log of a product is a sum

OpenStudy (anonymous):

let y = lim product (e^(k/n))*1/n for k = 0..n , take ln of both sides

OpenStudy (anonymous):

ln y = lim n-> oo sum k/n *1/n for k= 0..n , so ln y = integral 1/x from 0 to 1 ?

OpenStudy (anonymous):

my bad,

OpenStudy (anonymous):

ln y = integral x from 0 to 1

OpenStudy (anonymous):

ln [ lim n> oo [ e^0/n *e^(1/n) *e^(2/n)*...e^(n/n)] ^(1/n)] = lim ( 1/n (e^0/n + e^(1/n) + .. e^n/n)

OpenStudy (anonymous):

ln [ lim n> oo [ e^0/n *e^(1/n) *e^(2/n)*...e^(n/n)] ^(1/n)] = lim ( 1/n (e^0/n + e^(1/n) + .. e^n/n) , but this is not exactly a riemann sum

OpenStudy (anonymous):

a riemann sum should have n terms, this has n+1 terms

OpenStudy (anonymous):

i know im splitting hairs here but

OpenStudy (watchmath):

well, you can ignore the e^(0/n) since it is equal to 1.

OpenStudy (anonymous):

delta x = 1 - 0 / n , so delta x = 1/n

OpenStudy (anonymous):

hmmm, then its constant, then ...

OpenStudy (anonymous):

riemann sum is Sigma f ( a + r * delta x ) * delta x , for r = 1 to n , for right hand rule

OpenStudy (anonymous):

ln [ lim n> oo [ e^0/n *e^(1/n) *e^(2/n)*...e^(n/n)] ^(1/n)] = lim ( 1/n (e^0/n + e^(1/n) + .. e^n/n) = 1/n *1 + integral e^x for a = 0 to b = 1

OpenStudy (anonymous):

oh so that 1/n vanishes in the limit

OpenStudy (watchmath):

\(y=\left(\prod_{r=0}^n e^{r/n}\right)^{1/n}=\prod_{r=0}^n e^{r/n^2}\) \(\ln y=\sum_{r=0}^n \frac{r}{n^2}=\sum_{r=1}^n \frac{r}{n}\cdot \frac{1}{n}\) If we take the limit as \(n\to \infty\) then we have \(\int_0^1 x\, dx=1/2.\) So \(\lim y= \lim e^{\ln y}=e^{1/2}\)

OpenStudy (anonymous):

ln [ lim n> oo [ e^0/n *e^(1/n) *e^(2/n)*...e^(n/n)] ^(1/n)] = lim ( 1/n (e^0/n + e^(1/n) + .. e^n/n) = lim [ 1/n *1 + Sigma ( e^(r/n)*1/n , r=1..n ]

OpenStudy (anonymous):

oh woops

OpenStudy (anonymous):

ln [ lim n> oo [ e^0/n *e^(1/n) *e^(2/n)*...e^(n/n)] ^(1/n)] = lim ( 1/n ( 0/n + 1/n + 2/n + ... n/n) = lim [ 1/n *1 + Sigma (r/n)*1/n , r=1..n ]

OpenStudy (anonymous):

err, that should be zero the first term

OpenStudy (watchmath):

I see ... so you mean 1/n*0 right?

OpenStudy (anonymous):

ln [ lim n> oo [ e^0/n *e^(1/n) *e^(2/n)*...e^(n/n)] ^(1/n)] = lim ( 1/n ( 0/n + 1/n + 2/n + ... n/n) = lim [ 0 + Sigma (r/n)*1/n , r=1..n ] = integral

OpenStudy (anonymous):

yes

OpenStudy (watchmath):

Yes, that's right it is the same as what I wrote above :)

OpenStudy (anonymous):

hehe, i like my discrete proof though

OpenStudy (anonymous):

thanks a lot for your help with integration, i just have to practice a bit. and do lots of various scenarios . it helps to draw out the cylinder i guess

OpenStudy (anonymous):

my proof does not use fundamental theorem of calculus, so it may have an advantage

OpenStudy (anonymous):

the discrete approach

OpenStudy (watchmath):

Yes it helps to draw out the cyllinder. After some practices you won't need to draw the cyllinder explicitly :). So did you try the torus problem :).

OpenStudy (anonymous):

the shell integration is a bit diferent than washer or disc. since there is no inner and outer radius , like in those cases

OpenStudy (anonymous):

its just weird doing the whole 6 - x , when it revolves around say x = 6

OpenStudy (anonymous):

oh the torus, what was it again

OpenStudy (anonymous):

( x - R)^2 + y^2) ,

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