24. as shown in the figure, in the plane rectangular coordinate system, the image of quadratic function y=ax2+6x+c passes through point A (4 4,0) and point B (- 1 0), and intersects with the y axis at point c, point d is on the oc line, OD=t, point e is in the second quadrant, ∠ ade = 90.

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, EF⊥OD, vertical foot is F.

(1) Find the analytic expression of this quadratic function;

(2) Find the lengths OF line segments EF and of (expressed by algebraic expressions containing t);

(3) When ∠ECA=∠OAC, find the value of t. 。

25. As shown in the figure, in the fan-shaped AOB with radius of 2, ∠ AOB = 90, point C is the moving point (not coincident with points A and B) OD⊥BC, OE⊥AC on arc AB, and the vertical feet are D and E respectively.

(1) When BC= 1, find the length of line segment OD;

(2) Is there an edge with constant length in △ DOE? If it exists, please point out and find out its length; if it does not exist, please explain the reason;

(3) Let BD=x and the area of △DOE be y, find the functional relationship between y and x, and write its definition domain.