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I saw the following equations.

$$ \begin{align} \delta(ax) &= \frac {1} {\lvert a \rvert} \delta(x)\\ \delta(x^2-a^2) &= \frac {1} {2\lvert a \rvert} \left [ {\delta(x+a) + \delta(x-a)} \right ] \end{align}$$

I think the equation below is the general expression. Can someone let me know how the equation below is induced?

$$ \delta \left [ g(x) \right ]=\sum_i \frac { \delta(x-x_i) } { g'(x_i) } $$

Please don't use slang and abbreviations. I am not a native English speaker.

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Danny_Kim
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    you will find loads of proofs in the web: http://academic.reed.edu/physics/faculty/wheeler/documents/Miscellaneous%20Math/Delta%20Functions/Simplified%20Dirac%20Delta.pdf – tired Aug 25 '15 at 13:39
  • Thank you for a good document. :) I should print this out tomorrow, and read up. – Danny_Kim Aug 25 '15 at 13:42

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