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.