A Problem of my own device : - Algebra + Calculus

Calculate the value of " L " as depicted below -

Hint : - It is not as big as looks .

20 Answers

30
Ashish Kothari ·

Btw, I'm not your BHAIYA bhaiya! [3] lol. I'm have just come to class 12. :)

I don't know aren't all terms multiplied?

so like the first term under root is the 2/nth root of (n+1)/n which is further multiplied to 3/nth root of (n+1)/n which already under the 2/nth root.

Essentially what I mean is that isn't it,

L = \lim_{n\rightarrow\propto }\left( \frac{n+1}{n}\right)^n \left(\frac{n+1}{n} \right)^{\frac{1}{2/n}} \left(\frac{n+1}{n} \right)^{(\frac{1}{2/n})(\frac{1}{3/n})} .....

1
seoni ·

ricky..
check that u'll get

LOG{x} L= e-1........not x-1[think why!!]

though ans will remain same...e^(e-1)..coincidentaly:)

1
fibonacci ·

me too didnt get the step where ricky bhaiya took log
please explain

1
kunl ·

ricky i did not get what u did in the step where u took log of the series...cn u plz elaborate!

71
Vivek @ Born this Way ·

Yes.. now got it.. That was the only culprit (worm) that infected both of us - Nishant Sir and me :P

Ab toh abda aasan hai ! :P :P

If you more collection for good problem that I should try then please let me know. You may post them in my Chatbox. Plz

1
Ricky ·

No , if you look more closely . See , the " n - th " root of " x " = x 1 / n

Hence , suppose if you want the " 2n - th " root of " x " , that should be = x n / 2 .

62
Lokesh Verma ·

agree to vivek.. cos that is something that i also tried as soon as i saw the question...

I mean substituting it by x... b;ut that din help at all!

71
Vivek @ Born this Way ·

Ricky bhaiya, I have a serious doubt in your solution STEP 2# where you take

, .................. (i)

You have assumed ,

BUT In RHS of 1you are taking Index of root of x as 2,3,4 ....

Won't that be kind of xn3 , xn4 , Instead of what you have posted in the problem where Indexes of root are x3n, x4n ..

Correct me as It may be a serious problem for me.

1
Ricky ·

You don't sound foolish at all : )

Here goes my solution then : -

1
learner ·

is it ee

30
Ashish Kothari ·

= \lim_{n\rightarrow \propto }(\frac{n+1}{n})^{\sum{\frac{n^k}{k!}}}

= \lim_{n\rightarrow \propto } (1+\frac{1}{n})^{e^n-1}

= \lim_{n\rightarrow \propto } ((1+\frac{1}{n})^n)^\frac{e^n-1}{n}

= \lim_{n\rightarrow \propto } ((1+\frac{1}{n})^n) \lim_{n\rightarrow \propto } \frac{e^n -1}{n}

= ∞ [7]

1
Ricky ·

Sorry , that does equal the given expression . But still , it possesses some finite value .

30
Ashish Kothari ·

But isnt it,

L=\lim_{n\rightarrow\propto }\left( \frac{n+1}{n}\right)^n \left(\frac{n+1}{n}\right)^{n/2}\left( \frac{n+1}{n} \right)^{n^2/6} ...

71
Vivek @ Born this Way ·

May be I took it took the hint seriously :P Aur try karta hoo

71
Vivek @ Born this Way ·

Ricky Bhaiya, is any of these one answer to your sum :

e or 1

I have just tried to see. Let me know plz

62
Lokesh Verma ·

yaar kuch dikh to nahi raha :D

bata de kya gadbad hai :P

1
Ricky ·

Nishant sir and Ashish Bhai , are you sure what you have written are correct ? Please check once more on my behalf .

62
Lokesh Verma ·

srry it will be e to pwer infinity...

30
Ashish Kothari ·

okay..got the mistake sir.. Thanks! :)

62
Lokesh Verma ·

ashish.. the actual sum is

\left(\frac{n+1}{n} \right)^{n+n/2+n^2/3!+n^3/4!...} \\=\left(1+\frac{1}{n} \right)^{3n/2+n^2/3!+n^3/4!...} \\=\left(1+\frac{1}{n} \right)^{n(3/2+n/3!+n^2/4!...)} \\=\left(\left(1+\frac{1}{n} \right)^n\right)^{(3/2+n/3!+n^2/4!...)}

=e3/2

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