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Math Help - algebra help please

  1. #1
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    algebra help please

    Hi im wondering if you can help.


    f(x)= ax^2 +bx+c


    If f(1)=6, f(-1)=8 and f(-2)= 18. Find f(2)

    Note ^ means power of.
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  2. #2
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    The answer is f(2)=14. I dont know were the answer comes from, i was thinking simultaneous equations
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  3. #3
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    Quote Originally Posted by leavingcertmaths View Post
    Hi im wondering if you can help.


    f(x)= ax^2 +bx+c


    If f(1)=6, f(-1)=8 and f(-2)= 18. Find f(2)

    Note ^ means power of.
    Observe that:

    f(2) = f(-2) + 2(f(1) - f(-1))
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  4. #4
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    Quote Originally Posted by Isomorphism View Post
    Observe that:

    f(2) = f(-2) + 2(f(1) - f(-1))

    I understand that when you sub in the values for the equation above that you get that f(2)=14 but were did you get this equation?
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  5. #5
    Lord of certain Rings
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    The identity comes from substitution:

    f(2) = 4a+2b+c
    f(-2) = 4a -2b+c
    f(-1) = a - b+c
    f(1) = a+b+c
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