(2) Let the analytical formula of parabola be y = ax 2+bx+c, and substitute it into three coordinates of A, B and D to obtain the analytical formula of parabola:

y=- 1/2x ^2+x+4

(3) In quadrilateral ACEF, AC and EF are fixed, so as long as AF+CE is minimum, the perimeter of quadrilateral ACEF is also minimum. According to (2), the symmetry axis of parabola is x= 1. If point A is shifted upward to A 1 (-2, 1) and AF=A 1 E, it is the symmetry point A2 (4 4,4) of A1about the symmetry axis x= 1.

The minimum value of +CE is A2C, A2E=A 1E=AF, that is, AF+CE is the minimum.

A2C=√ 17, and the perimeter of the quadrilateral acef = AC+A2c+ef = 2 √ 2+√17+1.