25.( 12 points) (20 14? Quanzhou) as shown in the figure, AC>BC, AC > BC in acute triangle paper, and points D, E and F are on the sides of AB, BC and CA respectively. (1) known: DE∨AC, DF∨BC. 1 judgment?

What shape must the DECF of a quadrilateral be? 2 cutting?

When AC=24cm, BC=20cm, ∠ ACB = 45, please explore: how to cut the quadrangle DECF to maximize its area, and prove your conclusion; (2) folding?

Please use only two folds to determine the vertices d, e, c and f of the quadrilateral, so that it happens to be a diamond, and explain your folding method and reasons.