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Can someone help me solve this equation please? Watch

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    Here it is:

    x^3 - 61/32 x + 45/16 = 0

    I know the solutions ( 5/4 & -9/4) but I can't seem to get them
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    Start off multiplying by 32
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    (Original post by Dr. Django)
    Here it is:

    x^3 - 61/32 x + 45/16 = 0

    I know the solutions ( 5/4 & -9/4) but I can't seem to get them
    These are not solutions to this depressed cubic! Check by substitution?
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    (Original post by matty123)
    Start off multiplying by 32
    Nice attempt to pretend you have a clue what you are doing.
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    (Original post by Mr M)
    These are not solutions to this depressed cubic! Check by substitution?
    And there I was trying to help by using the factor theorem!
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    (Original post by matty123)
    And there I was trying to help by using the factor theorem!
    I'm sure there is a mistake earlier on unless the OP is trying to answer questions on numerical methods.
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    (Original post by Mr M)
    Nice attempt to pretend you have a clue what you are doing.
    Hey I just throught it was a standard cubic, and that is how I would go about solving cubics.
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    (Original post by Dr. Django)
    Here it is:

    x^3 - 61/32 x + 45/16 = 0

    I know the solutions ( 5/4 & -9/4) but I can't seem to get them
    After multiplying by 32, you could use polynomial division.

    This would suffice as you have to apply the factor theorem by inspection.

    On a side note, I must commend your taste in films
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    (Original post by Indeterminate)
    After multiplying by 32, you could use polynomial division.

    This would suffice as you have to use the factor theorem by inspection.
    What?!
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    5/4 definitely works with substitution? Anyways, generally, how do you solve equations of this form?
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    (Original post by Mr M)
    What?!
    I was suggesting division by, say

    (4x-5)

    after observing that 5/4 is a factor.

    I know, it's cheating, but you use trial and error to apply the factor theorem anyway.

    EDIT: on second thoughts, this might not work
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    (Original post by Indeterminate)
    I was suggesting division by, say

    (4x-5)

    after observing that 5/4 is a factor.

    I know, it's cheating, but you use trial and error to apply the factor theorem anyway.
    I see. Let me know when you find this linear factor.
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    Hm :/
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    (Original post by Dr. Django)
    5/4 definitely works with substitution
    I'm beginning to think I've gone quite mad.
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    (Original post by Mr M)
    I see. Let me know when you find this linear factor.
    I know you're a much loved figure on TSR, and I appreciate the help you usually give; but surely an attempt to help solve the equation would be more useful than the array of condescending remarks that your 'help' currently consists of.
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    (Original post by Dr. Django)
    I know you're a much loved figure on TSR, and I appreciate the help you usually give; but surely an attempt to help solve the equation would be more useful than the array of condescending remarks that your 'help' currently consists of.
    You don't seem to be listening to anything I'm saying and neither does anyone else.

    You have made a mistake. You are not trying to solve the equation you have posted. It can be solved but it is too difficult for the level you are working at. If you are studying a chapter on numerical methods, let me know and I will guide you through.
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    (Original post by Mr M)
    I see. Let me know when you find this linear factor.
    See my edit, but I've realised that it won't work. Plus the solutions the OP has given aren't correct

    Cubics aren't very nice to deal with, if I'm honest.

    I, for one, am not solving this the long way
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    (Original post by Indeterminate)
    the solutions the OP has given aren't correct
    I did say that at outset (post 3).
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    (Original post by Mr M)
    You don't seem to be listening to anything I'm saying and neither does anyone else.

    You have made a mistake. You are not trying to solve the equation you have posted. It can be solved but it is too difficult for the level you are working at. If you are studying a chapter on numerical methods, let me know and I will guide you through.
    Fair enough, im obviously approaching the question the wrong way. I'll restart and see if it I can do it; if not I'll be back thanks for your help
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    (Original post by Dr. Django)
    Fair enough, im obviously approaching the question the wrong way. I'll restart and see if it I can do it; if not I'll be back thanks for your help
    Ok. Would you like to post the previous working for me to check or is it too long?
 
 
 
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