Where is it from in Hunan? ? (20 1 1 Loudi City, Hunan Province)? 25. In the isosceles trapezoid ABCD, ad∨BC, AD=2, take CD as the diameter ⊙O 1, cross BC at point E, and cross E as EF⊥AB at point F, and establish a plane rectangular coordinate system as shown in the figure. It is known that the coordinates of point A and point B are A (0 0,2? )，B(-2，0)。

(1) Find the coordinates of c and d 。

(2) Verification: EF is the tangent of ⊙O 1.

(3) Question: As shown in the figure, is there a point P on the line segment CD, so that the length of the line segment PC is equal to the distance from the point P to the Y axis? If it exists, please find out the coordinates of point P; If it does not exist, please explain why.

(20 1 1 Zhuzhou city, Hunan province) 24. Kong Ming is a student who likes exploring and learning. When he and his classmates studied the properties of parabola y = ax2 (a < 0), they put the right-angled vertex of a right-angled triangle at the origin o of a plane rectangular coordinate system, and the two right-angled sides intersect the parabola at points A and B. Please answer the following questions:

(1) What if? (as shown in figure 1), find the value of a;

(2) For the same parabola, when Kongming rotates the triangle around point O to the position shown in Figure 2, B is taken as the BF⊥x axis of point F, and = 1 is measured, and the coordinates of point B at this time are recorded to find the abscissa of point A-4;

(3) For this parabola, when Kongming rotates the triangle around point O at any angle, he is surprised to find that the connecting line between intersection points A and B always passes through a fixed point. Try to explain why and find out the coordinates of this point.