По теореме синусов:
$$\frac{AB}{\sin C} = 2R$$
$$\frac{8\sqrt{2}}{\sin 45^\circ} = 2R$$
$$\frac{8\sqrt{2}}{\frac{\sqrt{2}}{2}} = 2R$$
$$8\sqrt{2} \cdot \frac{2}{\sqrt{2}} = 2R$$
$$16 = 2R$$
$$R = 8$$
Ответ: 8