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    • Thread Starter
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    Solve the following equation, give irration answers in terms of surds.

    x^4 - 5x^2 + 4 = 0

    therefore

    t^2 - 5t + 4 = 0

    Factorised as

    (t - 1)(t - 4)

    Therefore

    t = 1 or 4

    x = t^2 so

    x = 1 or 16.. WRONG

    so now i try putting t^2 - 5t + 4 = 0 into the quadratic formula

    again, t is 1 OR 4

    ...

    The answer in the book is saying +/- 1 OR +/- 2 ???

    Help please???

    Thanks,
    Sean
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    t doesn't equal x^2
    x^2 equals t

    (hope this helps )
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    x^2 = 1 or x^2 = 4

    You have squared. This is not the right thing to do to find x!

    Edit: I said t and meant x!
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    t = x^{2}

    So

    x = \sqrt{t}
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    (Original post by Mr M)
    x^2 = 1 or x^2 = 4

    You have squared. This is not the right thing to do to find t!
    what is right then?
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    (Original post by loopylouise)
    t doesn't equal x^2
    x^2 equals t

    (hope this helps )
    I know what you are trying to say but you haven't managed it!
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    (Original post by Bleak Lemming)
    what is right then?
    What operation "reverses" squaring?
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    (Original post by Mr M)
    I know what you are trying to say but you haven't managed it!
    ...rats... ah well, other people said it better... I'm gonna get some cafine
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    (Original post by StephenP91)
    t = x^{2}

    So

    x = \sqrt{t}
    Is there anything you would like to change about that last line?
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    (Original post by Mr M)
    Is there anything you would like to change about that last line?
    Besides plus or minus, but I have taken that as a given. That and I can't remember how to do it in LaTex.
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    (Original post by StephenP91)
    Besides plus or minus, but I have taken that as a given.
    Why have you taken that as given?
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    (Original post by Mr M)
    Why have you taken that as given?
    Look what I have said. I could have just typed it, but writing on this stupid IPod is effort as it is.
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    oh just give him the answer. He'll learn better when he realizes what simple mistakes he has done:

    (x^2 - 1)(x^2 - 4)

    x^2 = 1, 4.
    x = root(1 and root(4 = +/- 1 and +/- 2
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    (Original post by StephenP91)
    Look what I have said.
    Ah-ha.

    /pm in latex
    • Community Assistant
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    When solving equations of the form x^2 = k (where k is positive), about one quarter of AS students only find the positive solution.
 
 
 
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