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试题一、选择题(本题满分36分,每小题6分) 1．已知△ABC,若对任意t∈R,|BA- tBC|≥|AC|,则△ABC一定为( )．(A)锐角三角形(B)钝角三角形(C)直角三角形(D)答案不确定2．设logx(2x2+x-1)>logx2-1,则x的取值范围为( )．(A)1/21/2,且x≠1 (C)x>1 (D)00},a,b∈N,且A∩B∩N={2,3, 4),则整数对(a,b)的个数为( )．(A)20 (B)25 (C)30 (D)42 4．在直三棱柱A1B1C1-ABC中,∠BAC =π/2,AB=AC=AA1=1．已知G与E分别为A1B1和CC1的中点,D与F分别为线段AC和AB上的动点(不包括端点)．若GD⊥EF,则线段DF的长度的取值范围为( )．
Test questions, multiple-choice questions (the full 36 points of the question, each small question 6 points) 1. △ ABC is known. For any t∈R, | BA-tBC | ≥ | AC |, △ ABC must be (). (A) Sharp triangle (B) Obtuse triangle (C) Right triangle (D) The answer is uncertain 2. Let logx (2x2 + x-1)> logx2-1, the value of x is (). (A) 1/2 1/2, and x ≠ 1 (C) x> 1 (D) 0 0}, a, b∈N and A∩B∩N = {2,3,4) The number of (a, b) is (). (A) 20 (B) 25 (C) 30 (D) 42 4. In the straight prism A1B1C1-ABC, ∠ BAC = π / 2, AB = AC = AA1 = 1. It is known that G and E are the midpoints of A1B1 and CC1, respectively, and D and F are the moving points (excluding the endpoints) of segments AC and AB, respectively. If GD ⊥ EF, then the length of the line segment DF range ().