Compute the Laplace transform of f(t)=\cos (Rt-7) take R as 70

Albarellak

Albarellak

Answered question

2021-09-18

Compute the Laplace transform of f(t)=cos(Rt7) take R as 70

Answer & Explanation

Aamina Herring

Aamina Herring

Skilled2021-09-19Added 85 answers

Solution:
Given: f(t)=cos(Rt7) take R as 70
f(t)=cos(70t7)
Step 2
Note that cos(AB)=cosAcosB+sinAsinB
cos(70t7)=cos(70t)cos7+sin(70t)sin7
Now , L{f(t)}
=L{cos(70t7)}
=L{cos(70t)cos7+sin(70t)sin7}
=cos7L{cos(70t)}+sin7L{sin(70t)}
(sin7  and  cos7  are constants)
=cos7[ss2+(70)2]+sin7[70s2+(70)2]
(L{sinat}=as2+a2,L{cosat}=ss2+a2)
=scos(7)s2+4900+70sin(7)s2+4900
Hence, Laplace transform of f(t)=cos(70t7)  is  scos(7)+70sin(7)s2+4900

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