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Linear Equations

  1. Aug 5, 2009 #1
    Okay, so I expanded the brackets and simplified the equation from (x+4)(x-4)(x-4) to equal
    x3-4x2-16x+64 and I needed to sub those values into this equation y=ax3+bx2+cx-d where a=x3 b=-4x2 c=-16 d=64 which were the values I got from the first equation. I need confirmation If it would be y=x6[/SUP]-4x4-16x2-64
    I dunno, it just doesn't seem right.
     
  2. jcsd
  3. Aug 5, 2009 #2

    tiny-tim

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    Hi TheAkuma! :smile:

    Are you sure you don't mean a = 1, b = -4, c = -16, d = 64? :confused:

    What is the whole problem?
     
  4. Aug 5, 2009 #3
    I honestly don't know:confused: did you just ignore the 'x'?
     
  5. Aug 5, 2009 #4

    tiny-tim

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    Well, if x3-4x2-16x+64 is the same as y=ax3+bx2+cx-d, then a b c and d can't have any x in them.

    Or am I misunderstanding the question?
     
  6. Aug 5, 2009 #5
    What am I smoking? sorry about that. The question is already solved. I just had to expand the brackets into the form of y=ax3+bx2+cx-d which when solved is y=x3-4x2-16x-64 where 'a' in that equation would be 1 and 'b' would be '-4' and so on. Sorry about that
     
  7. Aug 5, 2009 #6

    tiny-tim

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    he he :biggrin:

    that's ok! :smile:
     
  8. Aug 6, 2009 #7
    uh oh. When I try to graph it on my calculator it comes up blank. Even though I spent one whole day trying to fix my graphics calculator. And when I try to do it manually, the parabola or whatever the hell its called is waay at the bottom of my graph. What am I doing wrong?
     
  9. Aug 6, 2009 #8

    tiny-tim

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    y = (x+4)(x-4)(x-4) is a cubic

    it goes up, down, and up …

    it cuts the x-axis at x = -4, goes up to about 100, comes down and touches the x-axis at x = 4, and goes up again …

    is that why it's off the graph?

    Try dividing everything by 10. :smile:
     
  10. Aug 7, 2009 #9
    Yeah, my calculator is being a retard so i made the scale the same as my mate's one which is the same model, only newer. Thanks for all your help tiny tim:cool: Now I can finish off my assignment:rofl:
     
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