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標題:

Ex7D :7,9,11,13

發問:

Ex7D 7,9,11,13 [IMG]http://i293.photobucket.com/albums/mm67/zaza520/0006-38.jpg[/IMG] [IMG]http://i293.photobucket.com/albums/mm67/zaza520/0007-34.jpg[/IMG] [IMG]http://i293.photobucket.com/albums/mm67/zaza520/0008-28.jpg[/IMG] [IMG]http://i293.photobucket.com/albums/mm67/zaza520/0009-20.jpg[/IMG]

最佳解答:

(7a) Let y = a/x2 + b where a and b are constants. When x = 1, y = -14, so a + b = -14 ... (1) When x = 3, y = 2, so a/9 + b = 2 ... (2) Solving, we have a = -18 and b = 4 (b) Sub x = 6: y = -18/62 + 4 = 7/2 (9a) Let V = a/h2 + bh where a and b are constants. When h = 2, V = 11, so a/4 + 2b = 11 ... (1) When h = 3, V = 26, so a/9 + 3b = 26 ... (2) Solving, we have a = -36 and b = 10 (b) Sub h = 6: V = -36/62 + 10(6) = 59 (11a) Let t = as2 + br where a and b are constants. When s = r = 2, t = 4, so 4a + 2b = 4 ... (1) When s = r = 5, t = 55, so 25a + 5b = 55 ... (2) Solving, we have a = 3 and b = -4 (b) Put s = 1 and r = 2, t = -5 (c) t = 3s2 - 4r -4 = 3s2 - 8s 3s2 - 8s + 4 = 0 (3s - 2)(s - 2) = 0 s = 2 or 2/3 (13a) Let T = ap2 + bpq where a and b are constants. When p = 2 and q = 3, T = 18, so 4a + 6b = 18 ... (1) When p = 4 and q = 11, T = 52, so 16a + 44b = 52 ... (2) Solving, we have a = 6 amd b = -1 (b) T = 6(5)2 - (5)(17) = 65 (c) 28 = 6p2 - 17p 6p2 - 17p - 28 = 0 (6p + 7)(p - 4) = 0 p = 4 or -7/6

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