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## Main Question or Discussion Point

Hi! I'm used to integrating over infinite spaces when working with QFT so far, but in an exercise I stumbled across a statement that

[tex] \int_V d^3x e^{-i \vec x \cdot (\vec p - \vec p')} = V \delta_{\vec p \vec p'} [/tex]

It is clear that this is okay when p = p', but it does not seem to make sence when this is not the case. I would however agree that it's approximately true when V is large. Is this what is meant by this statement? Is it a large V approximation?

[tex] \int_V d^3x e^{-i \vec x \cdot (\vec p - \vec p')} = V \delta_{\vec p \vec p'} [/tex]

It is clear that this is okay when p = p', but it does not seem to make sence when this is not the case. I would however agree that it's approximately true when V is large. Is this what is meant by this statement? Is it a large V approximation?