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Math Help - x and y intercepts.

  1. #1
    Member nautica17's Avatar
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    x and y intercepts.

    I need to find the x and y intercepts of this:

    f(x) = x^3 - 4x

    The y-intercept is just zero right? So how about the x's? I haven't done this in a while. Do you just factor this or do you do something else? I know it's easy.. but I'm having a major brain fade here. I'm guessing the x is on -4 and 4?

    Edit: I think I got it. x-intercepts are on (-2,0) and (2,0)?
    Last edited by mr fantastic; December 8th 2009 at 12:53 PM. Reason: rt --> de
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  2. #2
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    Quote Originally Posted by nautica17 View Post
    I need to find the x and y intercepts of this:

    f(x) = x^3 - 4x

    The y-intercept is just zero right? So how about the x's? I haven't done this in a while. Do you just factor this or do you do something else? I know it's easy.. but I'm having a major brain fade here. I'm guessing the x is on -4 and 4?

    Edit: I think I got it. x-intercepts are on (-2,0) and (2,0)?
    The y-intercept is given by f(0), so the y-intercept is zero. The x intercept is occurs when y=0=x^3-4x, so just solve this equation.
    Last edited by mr fantastic; December 8th 2009 at 12:54 PM.
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  3. #3
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    Quote Originally Posted by nautica17 View Post
    I need to find the x and y intercepts of this:

    f(x) = x^3 - 4x

    The y-intercept is just zero right? So how about the x's? I haven't done this in a while. Do you just factor this or do you do something else? I know it's easy.. but I'm having a major brain fade here. I'm guessing the x is on -4 and 4?

    Edit: I think I got it. x-intercepts are on (-2,0) and (2,0)?
    The x-intercepts are (x-2)(x+2) and 0.
    Last edited by mr fantastic; December 8th 2009 at 12:54 PM.
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  4. #4
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    Correction in red:
    Quote Originally Posted by Barthayn View Post
    The x-intercepts are the solutions to (x-2)(x+2)=0 and x = 0.
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