Calculate lim_(s -> 0) int_0^(+ oo) (e^(−st))/(1+t^2) dt

nyle2k8431

nyle2k8431

Answered question

2022-11-11

Calculate lim s 0   0 + e s t 1 + t 2   d t
lim s 0   0 + e s t 1 + t 2   d t
L { arctan ( t ) } = F ( s ) s
Final value theorem:
lim s 0   s F ( s ) = lim t + f ( t )
lim t +   arctan ( t ) = π 2
lim s 0     s   1 s F ( s ) = π 2
Is it correct?

Answer & Explanation

Zoey Benitez

Zoey Benitez

Beginner2022-11-12Added 18 answers

Your approach is correct, but why not use Lebesgue's dominated convergence theorem, for a shorter and simpler proof? Begin by noticing that e s t 1 + t 2 1 1 + t 2 and that, at the same time, | e s t 1 + t 2 | 1 1 + t 2 for all s 0, which is integrable. Then, Lebesgue's theorem guarantees that
0 e s t 1 + t 2 d t 0 1 1 + t 2 d t = π 2 .

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