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Math Help - Final in 2 hours, Zeros, amplitude, period etc

  1. #1
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    Final in 2 hours, Zeros, amplitude, period etc

    1. find the zeros of (x^2 + 2x - 7) (x^3 + 4x^2-21x)

    I got 0,-7,3 was hoping someone could do it and see if they get the same answer.

    2. x^4 + 6x^2 + 9
    I got no real zeros

    3. Find the amplitude, period and phase shift. y = cos(2t + pi/2)
    I got: amplitude = 1, period = pi, phase shift = pi/2

    Any help on any of them is EXTREMELY welcome. Thanks a million
    *edit* just put this in the pre calc help area seeing as I think I will get replys quicker and then noticed in the rules not to double post and I dont want to be a pest there a delete button for the entire thread?
    Last edited by Garface; December 9th 2008 at 10:23 AM.
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  2. #2
    MHF Contributor
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    Quote Originally Posted by Garface View Post
    1. find the zeros of (x^2 + 2x - 7) (x^3 + 4x^2-21x)

    I got 0,-7,3 was hoping someone could do it and see if they get the same answer.

    2. x^4 + 6x^2 + 9
    I got no real zeros

    3. Find the amplitude, period and phase shift. y = cos(2t + pi/2)
    I got: amplitude = 1, period = pi, phase shift = pi/2

    Any help on any of them is EXTREMELY welcome. Thanks a million
    *edit* just put this in the pre calc help area seeing as I think I will get replys quicker and then noticed in the rules not to double post and I dont want to be a pest there a delete button for the entire thread?
    Hi

    1. 0,-7,3 are the zeros of x^3 + 4x^2-21x but you have also to find the zeros of x^2 + 2x - 7

    2. OK since x^4 + 6x^2 + 9 = (x^2+3)^2

    3. OK
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  3. #3
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    For number one I didnt think there were any real zeros of the left hand side of the equation or at least not any that i could find. Graphing it I noticed that the parabola did cross the x axis but i tried using those numbers and it did not come out to exact zeros.
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  4. #4
    Member Greengoblin's Avatar
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    Have you tried the quadratic equation?

    x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}

    For a quadratic of the form:

    ax^2+bx+c
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