設數線上有一點\(P\)滿足\(P\)到\(1\)的距離加上\(P\)到\(4\)的距離等於\(4\)。試問這樣的\(P\)有幾個?(1) \(0\)個;(2) \(1\)個;(3) \(2\)個;(4) \(3\)個;(5) 無限多個
設點\(P\)表示的數為\(x\),則\(\vert x - 1\vert + \vert x - 4\vert = 4\)。當\(x \leq 1\)時,\(1 - x + 4 - x = 4\),解得\(x = \frac{1}{2}\);當\(1 < x < 4\)時,\(x - 1 + 4 - x = 3 \neq 4\),無解;當\(x \geq 4\)時,\(x - 1 + x - 4 = 4\),解得\(x = \frac{9}{2}\)。所以這樣的\(P\)有\(2\)個。答案:(3) 報錯
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