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