Finding Laplace Transform of te^(−t)

Cory Russell

Cory Russell

Answered question

2022-10-30

Finding Laplace Transform of t e t
I started with this integral:
0 e s t t e t d t = 0 t e ( s + 1 ) t d t
let d v = e ( s + 1 ) t d t , u = t and thus v = 1 s + 1 e ( s + 1 ) t d t , d u = d t
t s + 1 e ( s + 1 ) t | 0 + 1 s + 1 0 e ( s + 1 ) t d t = 1 ( s + 1 ) 2 e ( s + 1 ) t | 0
What mistakes have I made or do I just use L'Hopital's rule to finish?

Answer & Explanation

flasheadita237m

flasheadita237m

Beginner2022-10-31Added 17 answers

If you see an integral of the form
t f ( t ) d t
then try partial integration! Assuming s 1
0 t f ( t ) d t = [ t 1 s + 1 e ( s + 1 ) t ] t = 0 0 1 s + 1 e ( s + 1 ) t d t = 0 0 + [ 1 ( s + 1 ) 2 e ( s + 1 ) t ] t = 0 = 1 ( s + 1 ) 2
Tyson Atkins

Tyson Atkins

Beginner2022-11-01Added 1 answers

L { t e t } = 0 e s t t e t d t
= 0 e t ( s + 1 ) t d t
substitute
s t = x ; d t = d x s
= 1 s 2 0 x e x s ( s + 1 ) d x
x ( s + 1 ) s = m ; d x ( s + 1 ) s = d m ;
= 1 ( s + 1 ) 2 0 m   e m d m
= Γ ( 2 ) ( s + 1 ) 2
= 1 ( s + 1 ) 2

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