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1．在几何方面的应用例1 三棱锥A-BCD中,AB =AC=(13)~(1/2)/2,BC=CD=DB= 1,求AD的取值范围．分析如图1,设BC的中点为 E,连结AE、ED,易知
1. Application in geometry Example 1 In the triangular pyramid A-BCD, AB = AC = (13) ~ (1/2)/2, BC = CD = DB = 1, find the AD range. The analysis is shown in Fig. 1. Set the midpoint of BC to E and link AE and ED.