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help 發問於 科學及數學數學 · 8 年前

急! F5 about equations 1Cq02

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越詳細越好,唔該晒!

更新:

感謝你的回答,但21b點做 ?

1 個解答

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  • 8 年前
    最愛解答

    20.

    Let v km/h be Jack's original cycling speed.

    (30/v) - [30/(v + 3)] = 1/2

    [30(v + 3) - 30v] / [v(v + 3)] = 1/2

    90/(v² + 3v) = 1/2

    v² + 3v - 180 = 0

    (v - 12)(v + 15) = 0

    v = 12 or v = -15(rejected)

    Jack's original cycling speed = 12 km/h

    21.

    (a)

    Let n be the number of glassware bought by the students originally.

    (n - 2)[(48/n) + 3] - 48 = 22

    (n - 2)[(48/n) + 3] = 70

    (n - 2)[(48/n) + 3]n= 70n

    (n - 2)(48 + 3n)= 70n

    3n² - 28n - 96 = 0

    (n - 12)(3n + 8) = 0

    n = 12 or n - -8/3(rejected)

    Number of glassware bought by the students originally = 12

    22.

    20000 x (1 - 36%)^t - 11000 x (1 - 20%)^t = 3000

    20000 x 0.64^t - 11000 x 0.8^t = 3000

    20000 x 0.8^2t - 11000 x 0.8^t = 3000

    Let u = 0.8^t

    20000u^2 - 11000u = 3000

    20u^2 - 11u - 3 = 0

    (4u - 3)(5u + 1) = 0

    u = 3/4 or u = -1/5(rejected)

    0.8^t = 0.75

    t = log0.75/log0.8

    t = 1.289

    2012-08-16 22:13:18 補充:

    2.(b)

    Selling price of each piece of glassware

    = $[(48/12) + 3]

    = $7 ...... (ans)

    資料來源: wanszeto, wanszeto
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