Find the Laplace transform of NSK PSKf(t)=10e^{-200t}u(t)ZSK NSK Would it be correct to take

Patricia Crane

Patricia Crane

Answered question

2021-12-11

Find the Laplace transform of
f(t)=10e200tu(t)
Would it be correct to take out the 10 because it is a constant, find the Laplace transform of e200t and then multiply it by the Laplace transform of u(t) to obtain a final answer of
10(1s+200)(1s)
The u(t) is what is really confusing me in this problem.

Answer & Explanation

Mary Herrera

Mary Herrera

Beginner2021-12-12Added 37 answers

There is an extra 1/s in your final formula. Let f(t)=aebtu(t) with a,bR (I'm assuming your u(t) is the Heaviside step function). Then
(Lf)(s)=0f(t)estdt=0aebtestu(t)dt
=a0e(b+s)tdt=as+b
The region of convergence is sC:Re(s)b

Jenny Sheppard

Jenny Sheppard

Beginner2021-12-13Added 35 answers

It's OK to break out the 10 since the Laplace transform is linear, that is fox Lαf=α Lf for any constant α
But to separately transform e200t and u(t) and multiply the results is wrong. Multiplication under the L corresponds to convolution outside it.
However if you're talking about the one-sided laplace transform then the transform of e200tu(t) is the same as for e200t since we only integrate over positive numbers anyway. The result would consequently be:L10e200tu(t)=10Le200t=101s+200

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