Laplace transforms A powerful tool in solving

Chapter 7, Problem 80E

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QUESTION:

Laplace transforms A powerful tool in solving problems in engineering and physics is the Laplace transform. Given a function f(t), the Laplace transform is a new function F(s) defined by

\(F(s)=\int_{0}^{\infty} e^{-s t} f(t) \ d t\),

where we assume then s is a positive real number. For example, to find the Laplace transform oj f(t)= e?t, the following improper integral is evaluated using integration by parts:

\(F(s)=\int_{0}^{\infty} e^{-s t} e^{-t} \ d t=\int_{0}^{\infty} e^{-(s+1) t} \ d t=\frac{1}{s+1}\)

Verify the following Laplace transforms, where a is a real number.

\(f(t)=\cos a t \quad \ \rightarrow \quad \ F(s)=\frac{s}{s^{2}+a^{2}}\)

Questions & Answers

QUESTION:

Laplace transforms A powerful tool in solving problems in engineering and physics is the Laplace transform. Given a function f(t), the Laplace transform is a new function F(s) defined by

\(F(s)=\int_{0}^{\infty} e^{-s t} f(t) \ d t\),

where we assume then s is a positive real number. For example, to find the Laplace transform oj f(t)= e?t, the following improper integral is evaluated using integration by parts:

\(F(s)=\int_{0}^{\infty} e^{-s t} e^{-t} \ d t=\int_{0}^{\infty} e^{-(s+1) t} \ d t=\frac{1}{s+1}\)

Verify the following Laplace transforms, where a is a real number.

\(f(t)=\cos a t \quad \ \rightarrow \quad \ F(s)=\frac{s}{s^{2}+a^{2}}\)

ANSWER:

Solution

Step 1:

We have to verify the Laplace transform of cos at=

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