Find the Laplace transform F of the following functions and give the domain of F. f(x)=cos(2x)

kuCAu

kuCAu

Answered question

2021-09-23

The Laplace transform of a continuous function over the interval [0,)[0,) is defined by F(s)=0esxf(x)dx.
This definition is used to solve some important initial-value problems in differential equations, as discussed later. The domain of F is the set of all real numbers s such that the improper integral converges.
Find the Laplace transform F of the following functions and give the domain of F. f(x)=cos(2x)

Answer & Explanation

yunitsiL

yunitsiL

Skilled2021-09-24Added 108 answers

Since a continuous function's Laplace transform across the interval [0,) is defined by 
F(s)=0esxf(x) dx  
=0cos(2x)esx dx  
=limt0tcos(2x)esx dx  
By integrating by parts, we obtain
cos(2x)esx dx =1s2+4esr(2sin(2x)scos2x) 
Therefore
F(s)=limt(1s2+4esr(2sin(2x)scos2x)) 
=limt(ss2+41s2+4est(2sin(2t)tcos(2t))) 
=ss2+4 
Domain of F is [0,) 
Result
F(s)=1s 
Domain of F is [0,)

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