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Math Help - HELP.. someone

  1. #1
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    Smile HELP.. someone [Solved]

    Im stuck on this qustion:

    Draw a suitable straight line on the grid (a grid is provided) to find estimates of the solutions of the equation...

    x^2 - 3x - 6 = 0

    (^ means "to the power of", So... x(to the power of 2) - 3x - 6 =0 )

    Thanx to anyone who can help me out. i have no idear what to do
    Last edited by Stone Cold; March 27th 2008 at 05:22 AM. Reason: Clarify
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  2. #2
    Behold, the power of SARDINES!
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    Quote Originally Posted by Stone Cold View Post
    Im stuck on this qustion:

    Draw a suitable straight line on the grid (a grid is provided) to find estimates of the solutions of the equation...

    x^2 - 3x - 6 = 0

    (^ means "to the power of", So... x(to the power of 2) - 3x - 6 =0 )

    Thanx to anyone who can help me out. i have no idear what to do
    HELP.. someone-graph.bmp

    So the solutions that you are looking for are the x-intercepts.

    I would guess that they are about x=-1.4 and x=4.4

    Good luck.
    B
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  3. #3
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    Thats what i would have done, but the question asks me to "draw a suitable straight line" but the equation is quadratic WTF
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  4. #4
    Behold, the power of SARDINES!
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    Quote Originally Posted by Stone Cold View Post
    Thats what i would have done, but the question asks me to "draw a suitable straight line" but the equation is quadratic WTF

    My guess is they want you to find the equation of the line that passes though (-2,4) and (-1,-2) and use it to estimate by finding its x intercepts.

    This graph shows both the line(BLACK) and the parabola(RED).

    Good Luck.

    B
    HELP.. someone-both.bmp
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  5. #5
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    But why (-2,4) and (-1,-2)?
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  6. #6
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    If I had to take a stab at why the x-coordinates used were -2 and -1, I'd say because you can determine that the x-intercept is between those two x-values. Note that, for your original function, f(-2) is positive and f(-1) is negative. This means, since the function is continuous, i.e., doesn't have any holes, gaps, jumps, etc, that it must cross the x-axis somewhere between there. -2 and -1 provide nice integer values to use when creating your line of approximation.
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  7. #7
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    Quote Originally Posted by Stone Cold View Post
    But why (-2,4) and (-1,-2)?
    Because these are nice points where the parabola crosses the grid lines. (Of course you have to ensure that the line passes close to your zero!)

    -Dan
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  8. #8
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    No ofence guys, but the question seems to ask for one line.
    Yet using TheEmptySet idear seems to call for two stright lines to get both possible ansews.

    Here, i dont know if it will help but heres the question as it was on the exam paper.

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  9. #9
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    Drawing a single line to approximate BOTH "sides" of a parabola seems like an awful idea. I've got to assume the teacher meant one line per x-intercept. A single line could not possibly approximate both intercepts at once because a single line will only cross the x-axis ONCE (unless that line IS the x-axis, in which case it is equally useless as an approximation).
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  10. #10
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    Red face

    thanx everyone, this is from an IGCSE exam taken by thousands of pupils around the world. They try to be very clear in there questions. To stop problems such as these occurring.

    If no-one can reach an 100% sure answer, ill be going bk to school on next Tuesday ill post the answer here. tanx again
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  11. #11
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    You are given the graph of x^2 - 2x - 4

    If you want to find the solutions to the equation x^2 - 3x - 6 = 0

    Then rearrange to get:

    X^2 - 2x - 4 = x + 2

    The single line you want to draw is y = x + 2.
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  12. #12
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    Bravo. I think we were all stuck on finding the intercepts of the given quadratic, not using it to find the solutions to a different quadratic. Stellar.
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  13. #13
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    Talking

    Ting, thanks a million.
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