Two curves on a highway have the same radii. However, one is unbanked and the other is banked at an angle ?. A car can safely travel along the unbanked curve at a maximum speed v0 under conditions when the coefficient of static friction between the tires and the road is 0.980. The banked curve is frictionless, and the car can negotiate it at the same speed v0. Find the angle of the banked curve.