Find the value of
∫ 1 0 ( ln ( x 1 ) ) d x
If the answer is α input the value of ln α
Note
The d x is raised to the power. If you think that the given notation is meaningless, input 2 . 7 1 8
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Yes absolutely.........although, shouldn't you prove that the value of that integral is the euler mascheroni constant????
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@Aaghaz Mahajan That is quite a basic result, just substitute − ln x = t , You would get ∫ 0 ∞ ( ln t ) e − t d t . Now if I ( a ) = ∫ 0 ∞ t a − 1 e − t d t = Γ ( a ) then what we need is I ′ ( 1 ) = Γ ( 1 ) ψ ( 1 ) = − γ
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No no.......I know that already.....what I meant was, it would be better if you add this part in your solution :)
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@Aaghaz Mahajan – Yeah done.... edited the answer accordingly....
We can even advance this problem.
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Yeah, I mean Product Integrals were something new for me, and it just turns out to be a normal integration problem of a different function.....it is good if you can advance this!!
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It was too new for me. I advance it here . I even tried up doing generalization but I got stuck and didn't go further , haha.
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These type of integrals are called Multiplicative Integrals or Product Integral. The above integral is represented as ∏ 1 0 f ( x ) d x
Where f ( x ) = ln ( x 1 )
Using a property of Multiplicative integrals which is stated as a ∏ b f ( x ) d x = exp ( ∫ a b ln f ( x ) d x )
Thus in this case I = ∫ 1 0 ( ln ( x 1 ) ) d x = 1 ∏ 0 ( ln ( x 1 ) ) d x = exp ( ∫ 1 0 ln ( ln ( x 1 ) ) d x )
Now using that ∫ 0 1 ln ( ln ( x 1 ) ) d x = − γ
Where γ is the Euler Mascheroni Constant, we get I = exp ( ∫ 1 0 ln ( ln ( x 1 ) ) d x ) = e γ = α
Hence ln α = γ ≈ 0 . 5 7 7 2
Edit: Edit: Edit:
For the Evaluation of ∫ 0 1 ln ( ln ( x 1 ) ) d x
Just substitute − ln x = t , You would get ∫ 0 ∞ ( ln t ) e − t d t . Now if I ( a ) = ∫ 0 ∞ t a − 1 e − t d t = Γ ( a ) then what we need is I ′ ( 1 ) = Γ ( 1 ) ψ ( 1 ) = − γ