Compute int_0^(oo) (sin(x))/(xe^x)dx

lunja55

lunja55

Answered question

2022-09-24

Compute 0 sin ( x ) x e x   d x

Answer & Explanation

Guadalupe Reid

Guadalupe Reid

Beginner2022-09-25Added 8 answers

0 sin x x e x d x = 0 sin x 1 e s x d s d x = 1 0 sin ( x ) e s x d x d s = 1 L [ sin ( x ) ] ( s ) d s = 1 d s s 2 + 1 = π 2 tan 1 1 = π 4
Jase Rocha

Jase Rocha

Beginner2022-09-26Added 2 answers

Let
I ( a ) = 0 sin ( x ) x e a x d x
where your integral is I(1). I′(a) is then:
I ( a ) = 0 sin ( x ) e a x d x
which is the Laplace Transform of the sine function. Thus
I ( a ) = 1 a 2 + 1
Integrating back we get:
I ( a ) = arctan ( a ) + C
To find the constant, we notice that
I ( 0 ) = 0 sin ( x ) x d x = π 2
So we get that C = π 2 and that
I ( 1 ) = arctan ( 1 ) + π 2 = π 4

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