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Math Help - please help me to find K, Thanks

  1. #1
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    please help me to find K, Thanks

    If (x + 3) is a factor of x + kx - 8x + 48, find k.
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  2. #2
    Moo
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    Hello,

    Quote Originally Posted by tim_mannire View Post
    If (x + 3) is a factor of x + kx - 8x + 48, find k.
    Let f(x)=x^3+kx^2-8x+48.

    If (x+3) is a factor, then -3 is a root.

    Which means that f(-3)=0.

    Can you continue ?
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  3. #3
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    Quote Originally Posted by Moo View Post
    Hello,



    Let f(x)=x^3+kx^2-8x+48.

    If (x+3) is a factor, then -3 is a root.

    Which means that f(-3)=0.

    Can you continue ?
    yes I have done that, however, my peers have a few different answers to me. Do you know what K would would equal in this situation?
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  4. #4
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    Quote Originally Posted by tim_mannire View Post
    If (x + 3) is a factor of x + kx - 8x + 48, find k.
    when f(x) is divided by x-a, we have
    f(x) = (x-a)Q(x)+Remainder
    -> f(x) = (x-a)Q(x)+f(a)
    IF f(a) = 0, the remainder is 0.
    then f(x) = (x-a)Q(x)

    f(x) = x + kx - 8x + 48
    f(-3) = (-3)
    +k(-3)-8(-3)+48 = 0
    -27+9k+24+48 = 0
    9k = -45
    k = -5
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  5. #5
    Senior Member nikhil's Avatar
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    Lightbulb Check it out

    U should use factor theorem
    if x+3 is i factor of x^3+kx^2-8x+48 then on substituting x=-3 the value of polynomial will become equal to 0(u may ask why is that so in another thread or u may post it in the reply)
    therfor (-3)^3+k(-3)^2-8(-3)+48=0 or -27+9k+24+48=0
    or 9k=-45 therefor k=-5.
    Last edited by nikhil; June 25th 2008 at 11:30 PM. Reason: Mistake
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  6. #6
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    Quote Originally Posted by nikhil View Post
    U should use factor theorem
    if x+3 is i factor of x^3+kx^2-8x+48 then on substituting x=-3 the value of polynomial will become equal to 0(u may ask why is that so in another thread or u may post it in the reply)
    therfor (-3)^3+k(-3)^2-8(-3)+48=0 or -27+9k+24+48=0
    or 9k=45 therefor k=5.
    Please do not use U for ewe, or you or, .. Ewe will just confuse everyone otherwise.

    Also it is against the rules here to use l33t or text abreviations and if ewe do it habitualy ewe will start to collect infractions.

    RonL
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  7. #7
    Senior Member nikhil's Avatar
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    Sooooo...... Sorry

    Quote Originally Posted by CaptainBlack View Post
    Please do not use U for ewe, or you or, .. Ewe will just confuse everyone otherwise.

    Also it is against the rules here to use l33t or text abreviations and if ewe do it habitualy ewe will start to collect infractions.

    RonL
    sorry sir,next time this point will be kept in mind.
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