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F.4 QUADRATIC FUNCTIONS

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我既問題就在此圖中的21題 http://imageshack.us/photo/my-images/405/img1119l.jpg/ 請各大俠解救小弟

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Introducing a coordinate system into it, and supposing that the foot of the left post is the origin, we have: f(x) = 85 where f(x) = ax2 + bx + c, describing the function of the parabola Hence c = 85 f(450) = 85 a(450)2 + 450b + 85 = 85 450a + b = 0 ... (1) f(225) = 10 a(225)2 + 225b + 85 = 10 625a + 3b = -1 ... (2) Solving, we have a = 1/725 and b = -18/29 Thus: f(x) = x2/725 - 18x/29 + 85 For A and B, we have: A: x2/725 - 18x/29 + 85 = 37 x2 - 450x + 34800 = 0 x = 99.2 (since x < 225) B: x2/725 - 18x/29 + 85 = 58 x2 - 450x + 19575 = 0 x = 401.2 (since x > 225) Hence AB = 302 m

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