∫ 0 ∞ lo g x 3 1 + x 3 1 + x 3 x d x = M π lo g M − M 2 π N .
The equation above is true for M and N are positive integers. Find M + N .
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Nice method :)
Bonus: Can you generalize?
∫ 0 ∞ 1 + x n x a ln ( x m 1 + x n ) d x
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@hasan kassim Will you mind if I take this generalization to the Calculus Contest ?
But of course, then you will not be able to post the solution. But I have thought something so that you are not disadvantaged. Will you accept my proposal for being a staff member in this contest so that we both may post challenges(and then of course, when the contest ends, post the solutions(if required))?
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Of course I accept! My pleasure :)
You can post this generalization if you want , It is all yours!
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@Hasan Kassim – First of all thanks! I will try to wait.
Next of all, sorry I can't wait. This is the generalization-
n π c s c ( n π ( a + 1 ) ) ( n m π c o t ( n π ( a + 1 ) ) − ( ψ ( n n − a − 1 ) + γ ) )
Isn't it?
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@Kartik Sharma – Nope
you should take out the 1/n behind the digamma
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@Hasan Kassim – Yeah sorry. A big typo! I forgot that I have already taken that 1/n out. Now, is it fine?
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@Kartik Sharma – yes exactly !
Btw, did you solve it using complex??
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@Hasan Kassim – No. As usual I have used Ramanujan Master Theorem which is somehow a consequence of complex. I am yet to take a full course in complex. Just facing a time constraint! I know basic to intermediate level complex though. BTW, where did you learn complex?
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@Kartik Sharma – Actually I don't have any idea about complex analysis! That's why , as you can see, all my solutions are elementary and don't have any relation to complex... I have just learned the basics of complex; you know, the easy algebra topics. That's my domain in complex so far!!
I am trying to learn , but don't have a good book for complex :\
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@Hasan Kassim – Try this book: Complex Variables and Applications by Ruel .V. Churchill, James W. Brown and Roger F. Verhey. It's good.
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@Kishore S. Shenoy – Thanks Kishore!
Can you provide me a direct link?
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@Hasan Kassim – Link of what ⌣ ¨ ?
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@Kishore S. Shenoy – A link to reach the book or download link, isn't the book on the internet??
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@Hasan Kassim – http://bookfi.org/dl/1374590/ed64f7
@Hasan Kassim – I think you should check out Advanced Calculus - Wilfred Kaplan. It is not specifically a book for complex analysis(though it has a chapter named so) but it's a great book, seriously. Vectors, calculus, integration(line, surface etc.) etc. everything you would get interested in is in that book.
or if you can give me some time, tomorrow I will post the note , and you attach it to your set.
awsome method. only intuition would help! +1
You are 14, and how are you going to write JEE with us in 2017?
i thought about using this method. can we solve it using infinite series.
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Define
I ( a ) = ∫ 0 ∞ lo g x 3 a + x 3 1 + x 3 x d x
Then I ( 0 ) = 0 and
I ′ ( a ) = = = = = ∫ 0 ∞ ( a + x 3 ) ( 1 + x 3 ) x d x 3 1 ∫ 0 ∞ x 1 / 3 ( a + x ) ( 1 + x ) 1 d x 3 ( 1 − a ) 1 ( ∫ 0 ∞ x 1 / 3 ( a + x ) 1 d x − ∫ 0 ∞ x 1 / 3 ( 1 + x ) 1 d x ) 3 ( 1 − a ) 1 3 2 π ( a 1 / 3 1 − 1 ) 3 3 2 π a + a 2 / 3 + a 1 / 3 1
Here we use
∫ 0 ∞ x 1 / 3 ( a + x ) 1 d x = 3 a 1 / 3 2 π
Thus
I ( 1 ) = = = 3 2 π ∫ 0 1 a + a 2 / 3 + a 1 / 3 1 d a 3 3 2 π ∫ 0 1 b 2 + b + 1 b d b − 9 π 2 + 3 π ln 3 .