Integral of Complex exp of dot product

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SUMMARY

The integral of the complex exponential of the dot product, represented as S(𝑞) = ∫₀ʳ exp(i𝑞⋅𝑥)4π𝑥² dx, requires careful handling of the dot product in three-dimensional space. The discussion emphasizes the importance of switching to spherical coordinates, utilizing the volume element dV = r² sin(θ) dr dθ dφ, and recognizing the dot product as |𝑥||𝑞| cos(θ). Ignoring the dot product leads to incorrect results, highlighting the necessity of proper substitutions for accurate evaluation.

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[tex]S(\vec{q})= \int_0^r exp(i\vec{q}\cdot\vec{x})4\pi x^2 \ dx[/tex]

How would one approach this integral?
I tried to "ignore" the dot product and proceeded with [tex]exp(i\vec{q}\cdot \vec{x})=exp(iqx)[/tex] and got a wrong answer.
 
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If this integral is to be done in 3D, one may switch to spherical coordinates which has the volume element

[tex]dV = r^2 sin(\theta)\; dr\; d\theta\; d\phi[/tex]

and also, the dot product is

[tex]|x||q|\; cos(\theta)[/tex]

if x = r and play around with substitution, this integral might be easier to do.
 
Thanks!
 

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