Find the Laplace transform of f(t)=1+(1−t)u_1(t)+(t−2)u_3(t)

Eliza Gregory

Eliza Gregory

Answered question

2022-10-26

Find the Laplace transform of f ( t ) = 1 + ( 1 t ) u 1 ( t ) + ( t 2 ) u 3 ( t )

Answer & Explanation

Annabella Ferguson

Annabella Ferguson

Beginner2022-10-27Added 15 answers

f ( t ) = 1 + u 1 ( t ) t u 1 ( t ) + t u 3 ( t ) 2 u 3 ( t )
You need to take care with multiplication by t. The rule is L ( t t f ( t ) ) ( s ) = d f ^ ( s ) d s
Then (abusing notation slightly)
f ^ ( s ) = 1 s + 1 s e s ( d d s ( 1 s e s ) ) + ( d d s ( 1 s e 3 s ) ) 2 1 s e 3 s = 1 s + 1 s e s ( s + 1 ) s 2 e s + 3 s + 1 s 2 e 3 s 2 1 s e 3 s = 1 s 1 s 2 e s + ( s + 1 ) s 2 e 3 s
When you apply the transform, all 't's should disappear

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