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Math Help - Advanced Functions help... Determine an equation....

  1. #1
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    Advanced Functions help... Determine an equation....

    Determine an equation of a polynomial function with zeros at X= 2, -2, 1 and y-intercept of 24


    thanks in advanced!
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  2. #2
    Junior Member Mrdavid445's Avatar
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    Re: Advanced Functions help... Determine an equation....

    If your zeros are 2, -2, and 1, your polynomial can be written as y=(x-2)(x+2)(x-1)-a

    Since the y-intercept is 24, then 24=(0-2)(0+2)(0-1)-a

    So 24=4-a, and so a=-20

    Your polynomial would be y=(x-2)(x+2)(x-1)-20, and just expand the (x-2)(x+2)(x-1) part to get your final polynomial.
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  3. #3
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    Re: Advanced Functions help... Determine an equation....

    Quote Originally Posted by Mrdavid445 View Post
    If your zeros are 2, -2, and 1, your polynomial can be written as y=(x-2)(x+2)(x-1)-a
    Since the y-intercept is 24, then 24=(0-2)(0+2)(0-1)-a
    So 24=4-a, and so a=-20
    Your polynomial would be y=(x-2)(x+2)(x-1)-20, and just expand the (x-2)(x+2)(x-1) part to get your final polynomial.


    Actually that does not work. Look at this.

    This works: -6(x-2)(x+2)(x+1)
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  4. #4
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    Re: Advanced Functions help... Determine an equation....

    Hey MARZ.......
    THE SOLUTION DISCRIBED BY MRDAVID IS TOTALY WRONGGGGGGGGGGGGGGGGGGGGGGGGG !!!
    THE SOLUTION HE SUGGESTS (X-1)(X-2)(X+2)-20 GIVES A POLYNOMIAL X^3-X^2-4X-16....WHICH IS FAR FROM THE CORRECT ANSWER...

    THE MODERATORS OF THIS FORUM MUST CHECK THE ANSWERS FROM TIME TO TIME TO AVOID SUCH FALACIES....

    CORRECT SOLUTION:

    CONSTRUCT A POLYNOMIAL function OF 3RD DEGREE : f(x)= ax^3+bx^2+cx+d

    then f(0) = 24
    f(1) =0
    f(-2)=f(2) =0
    solve a system of 4 simultaneous equations to find the correct answer which is

    f(x) = 6x^3-6x^2-24x+24

    MINOAS
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