The length of the transverse axis of the rectangular hyperbola xy =18 is

Transverse axis is along the line y= x.
Solving y = x and xy =18, we have x² =18 or $\mathrm{x}=\pm 3\sqrt{2}$
Then the two vertices of the hyperbola are $(\pm 3\sqrt{2},\pm 3\sqrt{2})$
The distance between them is $\sqrt{72+72}=12$