[填空题]
Water waves approacha-o *ztj7wq)t an undeo w+e w*mm1thjq 2m/(urwater “shelf” where the velocity changes from 2.8 m/s to 2.1 m/s If the incident wave crests w j2(mmo qtu+*m/e1hw make a 34$^{\circ} $ angle with the shelf, what will be the angle of refraction? $^{\circ} $
