Lời giải:
Đặt $\frac{2}{3}x=\frac{3}{4}y=\frac{5}{6}z=t$
$\Rightarrow x=\frac{3}{2}t; y=\frac{4}{3}t; z=\frac{6}{5}t$
Khi đó:
$x^2+y^2+z^2=724$
$\Leftrightarrow (\frac{3}{2}t)^2+(\frac{4}{3}t)^2+(\frac{6}{5}t)^2=724$
$\Leftrightarrow \frac{4921}{900}t^2=724\Rightarrow t^2=\frac{724.900}{4921}$
$\Rightarrow t=\pm 30\sqrt{\frac{724}{4921}}$
$\Rightarrow (x,y,z)=(\pm 45\sqrt{\frac{724}{4921}}, \pm 40\sqrt{\frac{724}{4921}}, \pm 36\sqrt{\frac{724}{4921}}\right)$