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如图1,ABCD是一张矩形纸片,AD=BC=1,AB=CD=5,在矩形ABCD的边AB上取一点M,在CD上取一点N,将纸片沿MN折叠,使MB与DN交于点K,得到△MNK.(1)若∠1=70°,求∠MNK的度数.(2)如何折叠能够使△MNK的面积最小?若能,求出此时∠1的度数;若不能,试说明理由.(3)如何折叠能够使△MNK的面积最大?请你利用备用图探究可能出现的情况,求出最大值.(2011年威海中考试题)参考所能见到的的解答,(3)分两种情况:情况一:将矩形纸片对折,使点B与D重合,此时
In Figure 1, ABCD is a rectangular piece of paper, AD = BC = 1, AB = CD = 5, take a point M on the side AB of the rectangle ABCD, take a point N on the CD, fold the sheet along MN, so that MB and DN intersect at point K to obtain △MNK. (1) If ∠1=70°, find the degree of MNK. (2) How can the folding minimize the area of △MNK? If yes, find the value of ∠MNK. Degrees; if not, try to explain the reason. (3) How can the folding maximize the area of △MNK? Please use alternate graphs to explore possible situations and find the maximum value. (Weihai Middle School Examination Questions 2011) Reference can be seen The answer to (3) is divided into two cases: Case 1: Fold the rectangular papers so that the points B and D coincide.