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Math Help - Second degree equation (difficult)

  1. #1
    Newbie Bluerabbits's Avatar
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    Exclamation Second degree equation (difficult)

    C) x^3 - 8x^2 + 15x = 0

    I donīt know how to solve this the formulae I usually use I canīt use it since it is x^3 and not x^2... I donīt know what the formulae is called in English.


    D) 4(3-3x) (8-2x^2)= 0

    Help anyone? :/
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  2. #2
    A Plied Mathematician
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    For C, factor out an x on the LHS. That corresponds to the solution x = 0. Then what remains is a quadratic, for which there are numerous methods of solution. For D, each factor could be zero, so solve them separately.

    Make sense?
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  3. #3
    Newbie Bluerabbits's Avatar
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    Quote Originally Posted by Ackbeet View Post
    For C, factor out an x on the LHS. That corresponds to the solution x = 0. Then what remains is a quadratic, for which there are numerous methods of solution. For D, each factor could be zero, so solve them separately.

    Make sense?
    Yes, it does. =) Just unsure how to solve D... I tried but failed.
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  4. #4
    Flow Master
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    Quote Originally Posted by Bluerabbits View Post
    Yes, it does. =) Just unsure how to solve D... I tried but failed.
    What did you try? Please show all your working. I hope part of your effort involved the null factor law.
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  5. #5
    Newbie Bluerabbits's Avatar
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    Quote Originally Posted by mr fantastic View Post
    What did you try? Please show all your working. I hope part of your effort involved the null factor law.
    4(3-3x)(8-2x^2)=0
    I just divided 4 and then I got:

    (3-3x)=0 or (8-2x^2)=0

    (3-3x)=0
    x=1

    (8-2x^2)=0
    2(4-x^2)=0
    4-x^2 = 0
    x=ą2
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  6. #6
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    Quote Originally Posted by Bluerabbits View Post
    4(3-3x)(8-2x^2)=0
    I just divided 4 and then I got:

    (3-3x)=0 or (8-2x^2)=0

    (3-3x)=0
    x=1

    (8-2x^2)=0
    2(4-x^2)=0
    4-x^2 = 0
    x=ą2
    So why did you say you "tried but failed"?
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  7. #7
    Newbie Bluerabbits's Avatar
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    Well in the beginning I was unsure how to approach the number and I didnīt get the right answer. Then I got some help and understood what I did wrong. =)
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