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Hi,

I have a double (actually quadruple, but the other dimensions don't matter here) integral which looks like this:

[tex] \iint_0^\infty \frac{d^2 k}{k^2} [/tex]

Now, someone here told me to replace that with

[tex] \int_0^\infty \frac{1}{2} 2\pi \frac{d k^2}{k^2} [/tex]

How and why is this ok? Thanks!

PS: For anyone wondering where this comes up: it's related to Elementary Particle physics and structure function calculation.

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# Double integral to single by magic substitution

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