372. Find the condition under which the numbers $a, b, c, d$, taken in any order, form consecutive terms of a geometric progression.
If the numbers $a, b, c, d$, taken in any order, form consecutive terms of a geometric progression, then $\frac{a}{b}=\frac{c}{d}$ and $\frac{a}{b}=\frac{d}{c}$, from which $\frac{a^{2}}{b^{2}}=1$ and $a= \pm b$. Similarly,
$b= \pm c, c= \pm d$, i.e., all four numbers must be equal in absolute value.