Find the Laplace transform of g(t)=1+cos^2(2t) by direct integration

Humberto Campbell

Humberto Campbell

Answered question

2022-11-08

Find the Laplace transform of g ( t ) = 1 + c o s 2 ( 2 t ) by direct integration
I'm having trouble finding out how to directly integrate the function f(t) because of the cos 2 ( 2 t ) term. I understand that cos 2 ( 2 t ) = 1 2 + 1 2 cos ( 4 t ) but I don't understand how this simplifies the problem so that
0 e s t + 0 e s t ( 1 2 + 1 2 cos ( 4 t ) )
Is an easier integral to solve.

Answer & Explanation

Teagan Raymond

Teagan Raymond

Beginner2022-11-09Added 14 answers

You have that cos ( 4 t ) = e 4 i t so
0 e s t cos ( 4 t ) d t = 0 e ( s + 4 i ) t d t = e ( s + 4 i ) t s + 4 i | t = 0 t = = 1 s + 4 i = s + 4 i s 2 + 16 = s s 2 + 16

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