Solution
= Solution
For every test <function> $\varphi$ and nonzero $p$, substitution $u=pt$ with the orientation handled by $|p|$ gives
$$
\int\varphi(t)\delta(pt)dt=\frac1{|p|}\varphi(0).
$$
\b[Hence the <Dirac delta scaling> identity is $\delta(pt)=\delta(t)/|p|$.]