As shown in the figure, in the plane rectangular coordinate system xoy, the analytical expression of the parabola is

As shown in the figure, in the plane rectangular coordinate system xoy, the analytical expression of the parabola is

solution
(1) Let the analytic formula of parabola be y = a (x-1) (X-5), and substituting a (0,4) into it, the solution is a = 4 / 5. The analytic formula of parabola is
Y = 4 (x-1) (X-5) / 5 = 4 (x-3) ^ 2 / 5-16 / 5, x = 3
(2) The coordinates of point P (6,4)
(3) Let n [x, 4 (x-4 (x-4 (x-4 (x-4 (x-4 (x-3) (x-3 (x-3) (x-3) ^ 2 / 5-5-16 / 5], then E (x, - 4x / 5 + 4) is e (x, - 4x / 5 + 4), so en = - 4X / 5 + 4 - [4 (x-3) ^ 4 (4 (x-3) ^ 4 (x-4 (x-3) ^ 2 / 4 (4 (x-3) (4 (x-3) (4 (x-3) (4 (x-3) ^ 4 (4 (4 (x-3) ^ 4 (4 (4 (x-3) ^ 4 (4 (4 (x-3) ^ 4 (4 (4 (x-3) (4 (x-3) (4 (x-3) (4 (x-3) ^ 2 (x-3) ^ 2 / 2 / 2 / 2 / 3) ^ 2 / 2 / 2 / 5) / 2 / 5) / 2 / 5 when the coordinates are (5 / 2, - 3), the maximum area of △ NAC is 25 / 2
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