Saturday, May 23, 2009

Chapter 3 Question 1

Given that y=px^2+qx passes through(6,0) and has a minimum value of -12.Find the value of p and q.

10 comments:

  1. 1st, pluck in the (6,0) in the equation y = px^2 + qx,
    0 = 36p + 6q
    0 = 6p + q ... (1)

    then, complete the square of the equation,
    y = p(x^2 + qx/p)
    = p[x^2 + qx/p + (q/2p)^2 - (q/2p)^2]
    = p[(x + qx/2p)^2 - (q/2p)^2]
    = p(x + qx/2p)^2 - p(q/2p)^2

    p(q/2p)^2 = -12
    -q^2/4p = -12
    q^2 = 48p ... (2)

    From (1)
    q = -6p ... (3)

    Pluck in (3) into (2)
    36p^2 = 48p
    36p^2 - 48p = 0
    12p(3p - 4) = 0

    so, p = 0 or p = 4/3

    pluck in p = 4/3 into (3)
    q = -8

    Any question?

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  3. Good then, study hard and good luck!

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  4. 今天的add math&chemi都不会做啊~~

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  5. Haha it's ok lah, just study hard and concentrate on others subject! Add oil!

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  6. Huh!? Which Kong are you? And What is so funny? Haha

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