EA and EB are equal, so it is an isosceles triangle. So make the fish have a top angle of 90 degrees. That is, the vertex angle of cos is greater than 0, or half of the vertex angle of cos is greater than two-thirds of the root sign. F is the focus, then you can get A by substituting -c, and the ordinate of point B is plus or minus B divided by A, and then according to the properties of hyperbola, you can calculate it yourself later. .