Inverse Laplace transform of L^(-1)((a)/((s^2+a^2)^2)). Hence show that int_0^(oo) t^3 e^(-t)sin t dt=0

Nathalie Case

Nathalie Case

Answered question

2022-10-14

Inverse Laplace transform of L 1 ( a ( s 2 + a 2 ) 2 ) . Hence show that 0 t 3 e t sin t d t = 0
My attempt:
L ( t cos t ) = 0 e p t ( t cos t ) d t
Now evaluating this and putting p = 2, i get answer as 3/25
Now can you tell me is there any alternative way to evaluate this?
Problem says hence show 0 t 3 e t sin t d t = 0
The integral = L ( t 3 sin t ) = 0 t 3 e p t sin t d t = ( 1 ) d 3 d p 3 1 p 2 + 1 = 8 p ( p 2 1 ) 2 + 48 p 3 ( p 2 1 ) 4
Now putting p =1 does not make sense in above equation. How to deal with this?

Answer & Explanation

Martha Dickson

Martha Dickson

Beginner2022-10-15Added 20 answers

Note that we are differentiating 1 1 + p 2 , so how do you get a −1 in the denominator?
The correct value of:
( 1 ) d 3 d p 3 ( 1 1 + p 2 ) = 24 p ( p 2 1 ) ( p 2 + 1 ) 4
which at p=1 is zero.

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