Laplace transform of int_t^(oo) psi(tau)d tau

figoveck38

figoveck38

Answered question

2022-11-18

Why this equality?
L ( t + ψ ( τ ) d τ ) = 1 ψ ( s ) s
Can you help me with the steps?

Answer & Explanation

jennasyliang4tr

jennasyliang4tr

Beginner2022-11-19Added 15 answers

Denoting Ψ ( t ) = t ψ ( τ ) d τ, we have by definition of L, that
L ( Ψ ) ( s ) = 0 exp ( s t ) Ψ ( t ) d t = 0 exp ( s t ) t ψ ( τ ) d τ d t = 0 t exp ( s t ) ψ ( τ ) d τ d t = 0 0 τ exp ( s t ) ψ ( τ ) d t d τ = 0 0 τ exp ( s t ) d t ψ ( τ ) d τ = 0 ( 1 s 1 s exp ( s τ ) ) ψ ( τ ) d τ = 0 ψ ( τ ) d τ L ( ψ ) ( s ) s
So your equation is true, if 0 ψ ( τ ) d τ = 1 and L ( ψ ) = ψ

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