As shown in the figure, the cylindrical nozzle OA is vertically installed in the center of the circular fountain, and the nozzle at A sprays water outward, and the water flows down along the parabolic trajectory with the same shape in all directions. According to the rectangular coordinate system shown in the figure, the relationship between the height y(m) of water jet and the horizontal distance x(m) is y =-x 2+2x+7/4 (x >: 0). What is the height of OA column? If other factors are not considered, how many meters should the radius of the pool be at least, so that the sprayed water will not fall outside the pool? (Results Retain the root number)