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Math Help - Functions! f(x)=

  1. #1
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    Functions! f(x)=

    ok so i have my core 1 exam on friday and am struggling with SOME functions.

    i am at work and dont have the question for reference but its alogn the lines of

    (x-2) is a factor of f(0)

    find the values of k and c in f(x)=2x^2+kc+c

    thanks in advance
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  2. #2
    Super Member craig's Avatar
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    I'm not sure but did you mistype your question, I think it should be something like:
    f(x)=2x^2+kx+c

    Can you remember what other information you are given about the roots of the equation?

    With questions like these you usually use the discriminant, b^2-4ac.

    For equal roots, b^2-4ac=0
    For diffferent real roots, b^2-4ac >0
    For no real roots, b^2-4ac<0

    I know this doesn't answer your question but hope it helps you when you have the actual question in front of you
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  3. #3
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    information

    it very possibly said somethign along the lines of f(x)=6

    if that doesn't mean anything i will have al ook when i get home and retype on this post with the whole question and how it is worded
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  4. #4
    Super Member craig's Avatar
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    Yeh post the actual question when you get home and I'll try and get my head round it then
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  5. #5
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    the actual question!

    You are given that f(x) = x^3 + kx +c. The value of f(0) is 6, and x-2 is a factor of f(x).

    find the values of k and c




    there we go, helps to have what your asking in front of you lol, thanks in advance
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  6. #6
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    Quote Originally Posted by coyoteflare View Post
    You are given that f(x) = x^3 + kx +c. The value of f(0) is 6, and x-2 is a factor of f(x).

    find the values of k and c




    there we go, helps to have what your asking in front of you lol, thanks in advance
    f(0) = 6 => 6 = c.

    (x - 2) is a factor => f(2) = 0 => 0 = 2^3 + 2k + c

    And now you should be able to finish this.
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  7. #7
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    thanks, can you explain to me why c is 6? is it to do with >0 and <0 ?

    0 = 2^3 + 2k + 6

    0 = 8 + 2k + 6

    -14 = 2k

    -7 = k ?

    thanks again
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  8. #8
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    Quote Originally Posted by coyoteflare View Post
    thanks, can you explain to me why c is 6? is it to do with >0 and <0 ?

    0 = 2^3 + 2k + 6

    0 = 8 + 2k + 6

    -14 = 2k

    -7 = k ? Mr F says: yes.

    thanks again
    f(x) = x^3 + kx +c. The value of f(0) is 6
    Therefore 6 = 0^3 + k(0) + c ......
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  9. #9
    Super Member craig's Avatar
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    Ah this isn't as hard as I first thought

    You have the following equation

    x^3 + kx +c

    and you are told that f(0) = 6

    You can therefore work out that then you sub 0 into the equation it equals 6, giving you:

    0^3 + 0k +c = 6

    therefore c = 6

    Reading on from this you are told that x - 2 is a factor, therefore subbing 2 into the equation will give you zero.

    2^3 + 2k + 6 = 0

    The rest I'm sure is clear

    Hope this explains it

    Craig
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  10. #10
    Super Member craig's Avatar
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    Sorry I've got beaten to the answer
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  11. #11
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    Thanks guys!

    not as hard as i thought, just never had functions explained to me an got confused xD

    thanks again!
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