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Math Help - Evaluating a function

  1. #1
    Member M670's Avatar
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    Evaluating a function

    I have been trying this for 2 days and I can"t seem to get the right answer \

    when f(x) =(x+1)
    and f(x) = (-x)
    when its (x-1) i get the following
    2(x-1)^2 +7(x-1)-8
    2x^2-4x+2+7x+7x-8
    2x^2+3x-1 Is my solution right?

    And -X i am just not sure I got 2x^2-8x-8 this as my answer
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  2. #2
    MHF Contributor Siron's Avatar
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    Re: Evaluating a function

    I get:
    f(x-1) = 2(x-1)^2+7(x-1)-8 = 2(x^2-2x+1)+7x-7-8 = 2x^2-4x+2+7x-15 = 2x^2+3x-13
    f(-x)=2(-x)^2+7(-x)-8=2x^2-7x-8
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  3. #3
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    Re: Evaluating a function

    Quote Originally Posted by M670 View Post
    I have been trying this for 2 days and I can"t seem to get the right answer \

    when f(x) =(x+1)
    and f(x) = (-x)
    when its (x-1) i get the following
    2(x-1)^2 +7(x-1)-8
    2x^2-4x+2+7x+7x-8
    2x^2+3x-1 Is my solution right?And -X i am just not sure I got 2x^2-8x-8 this as my answer
    I don't understand what you are to do.

    If f(x)=2x^2+7x-8 then
    f(x+1)=2(x+1)^2+7(x+1)-8=2x^2+4x+2+7x+7-8=2x^2+11x+1.
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  4. #4
    Member M670's Avatar
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    Re: Evaluating a function

    Sorry i Corrected my formula it was (x+1) not (x-1) I believe it changes the answer to mine
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  5. #5
    Member M670's Avatar
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    Re: Evaluating a function

    Quote Originally Posted by Plato View Post
    I don't understand what you are to do.

    If f(x)=2x^2+7x-8 then
    f(x+1)=2(x+1)^2+7(x+1)-8-=2x^2+4x+2+7x+7-8=2x^2+11x+1.
    The question is simply to evaluate the function in regards to F(x) being f(x+1) or f(-x) or even f(-5) and inputting it in the formula f(x)=2x^2+7x-8
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  6. #6
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    Re: Evaluating a function

    Quote Originally Posted by M670 View Post
    The question is simply to evaluate the function in regards to F(x) being f(x+1) or f(-x) or even f(-5) and inputting it in the formula f(x)=2x^2+7x-8
    That does not change what I posted.
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  7. #7
    Member M670's Avatar
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    Re: Evaluating a function

    Quote Originally Posted by Plato View Post
    That does not change what I posted.
    your answer? or you not understanding what I am doing?
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  8. #8
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    Re: Evaluating a function

    Quote Originally Posted by M670 View Post
    your answer? or you not understanding what I am doing?
    Here is the answer to the first part of the OP.
    If f(x)=2x^2+7x-8 then
    f(x+1)=2(x+1)^2+7(x+1)-8=2x^2+4x+2+7x+7-8=2x^2+11x+1.
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  9. #9
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    Re: Evaluating a function

    I think you mean that you are given that f(x)= 2x^2+ 7x- 8 and you are asked to evaluate f(x+ 1) and f(-x) though that is not at all what you are saying in your initial post or post #5.

    f(x+1)= 2(x+1)^2+ 7(x+1)- 8 and f(-x)= 2(-x)^2+ 7(-x)- 8.
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