Need to find Laplace transform of this f(t) f(t)=(e^(at)−cos bt)/(t)

Teagan Huffman

Teagan Huffman

Answered question

2022-09-24

I need to find Laplace transform of this f(t)
f ( t ) = e a t cos b t t
My approach:
F ( s ) = L ( e a t t ) L ( Re ( e i b t t ) )
But I don't know how to solve such cases

Answer & Explanation

pagellera10

pagellera10

Beginner2022-09-25Added 7 answers

That approach can't work, because e a t / t does not have a Laplace transform, because 0 1 e a t / t d t =
More or less as already suggested, if F ( s ) = L [ f ] then L [ t f ( t ) ] = F ( s ). This allows you to find F ( s ), which gives you F(s) up to a " + c "". Then you can find the value of c by considering what happens as s +
Amaris Orr

Amaris Orr

Beginner2022-09-26Added 2 answers

0 [ e a t cos ( b t ) t ] e s t d t = 0 e ( s a ) t e ( s i | b | ) t t d t =   ( 0 ln ( t ) { e ( s a ) t [ ( s a ) ] e ( s i | b | ) t [ ( s i | b | ) ] } d t ) (1) =   [ 0 ln ( t s a ) e t d t 0 ln ( t s i | b | ) e t d t ] =   [ ln ( s a ) + ln ( s i | b | ) ] = 1 2 ln ( s 2 + b 2 ) ln ( s a )

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