Show using Laplace Transform that: int_0^(oo) cos(x^2)dx=1/2 sqrt((pi)/(2))

Kailyn Hamilton

Kailyn Hamilton

Answered question

2022-11-11

Show using Laplace Transform that:
0   cos ( x 2 )   d x = 1 2 π 2
The right hand side seems like it has something to do with the gamma function. Help with it please!

Answer & Explanation

Kayleigh Cross

Kayleigh Cross

Beginner2022-11-12Added 19 answers

In the improper-Riemann sense,
0 + cos ( x 2 ) d x = 0 + cos ( x ) 2 x d x = 1 2 π 0 + s 1 + s 2 d s = 1 π 0 + u 2 1 + u 4 d u
where the middle equality is due to L ( cos x ) ( s ) = s 1 + s 2 and L 1 ( 1 2 x ) ( s ) = 1 2 π s (s)=12πs√.The last integral can be computed through standard techniques (for instance, partial fraction decomposition) and it equals π 2 2 , proving the claim.

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