Why do these terms vanish in this solution?

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Homework Statement



I was given this problem as homework and managed to find the solution online, but I don't fully understand it.

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My only question, and the reason I was getting this problem wrong, is because I wasn't realizing that the functions evaluated from -∞ to +∞ were vanishing. Is this a concept from calculus I'm not understanding or is this related somehow to a QM postulate or something?

Thanks!
 
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That condition is just a physicality condition on f. f is a wave function so the physical interpretation of this is that any wave function or derivatives of wave functions must vanish or be zero at infinity. Its kind of like an electric field due to a charge source being zero really far away from the charge source. Its a simplifying assumption.
 


Ah, thanks.
 

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