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Math Help - Derived Functions

  1. #1
    Senior Member sakonpure6's Avatar
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    Derived Functions

    Hi, we have f(x)=2x and g(x)=x^2-15, what is (f-g)(-3). And this is a multiple choice question with the following answers :
    a) -12
    b) -6
    c) 0
    d) 30

    I first found out (f-g) which = (x-5)(x+3)

    Then this means that (x-5)(x+3)(-3). Since (f-g)(-3).

    What next? Is this all the question is asking? I know the zeros 5 and -3 and we have the other value of -3. Now what?
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  2. #2
    MHF Contributor
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    Re: Derived Functions

    Hey sakonpure6.

    What exactly is f-g? Is it f(x) - g(x) or is it f(g(x)) or g(f(x))?

    If indeed it is f-g = (x-5)(x+3) then (f-g)(-3) is evaluating f-g at x = -3 in which case you can do the substitutions and see the answer (it is one of the options given).
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