Find ccL{cos^3(t)}

Hayley Mcclain

Hayley Mcclain

Answered question

2022-11-04

Find L { cos 3 ( t ) }

Answer & Explanation

takwerkyo0

takwerkyo0

Beginner2022-11-05Added 17 answers

Hint :
Use triple-angle formula:
cos 3 t = cos 3 t + 3 cos t 4
Kayley Dickson

Kayley Dickson

Beginner2022-11-06Added 3 answers

One option is to use the complex identity
cos t = 1 2 ( e i t + e i t ) ,
which gives
cos 3 t = 1 8 ( e 3 i t + 3 e i t + e i t + e 3 i t ) = 1 4 [ 1 2 ( e 3 i t + e 3 i t ) + 3 1 2 ( e i t + e i t ) ] = 1 4 ( cos 3 t + 3 cos 3 t ) ,
which reduces the computation to the standard integral
e u cos a u d u .

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