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Math Help - how to find the derivatives

  1. #1
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    how to find the derivatives


    1. f(x)=((x+1)(x-2))/(x^2 -5x +1)
    2. f(x)= (x2 − 1)(x^3 + 3x^2/x^2 + 2)

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  2. #2
    Junior Member plm2e's Avatar
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    Quote Originally Posted by henri View Post
    1. f(x)=((x+1)(x-2))/(x^2 -5x +1)
    2. f(x)= (x2 − 1)(x^3 + 3x^2/x^2 + 2)

    Quotient Rule:

    y = f(x)/g(x)
    y' = [g(x) f '(x) - f(x) g'(x)]/ [g(x)]^2

    in prob 1: do: y = ((x+1)(x-2))/(x^2 -5x +1)

    your f(x) is: (x+1)(x-2) or: (x^2 -x -2)

    your g(x) is: (x^2 -5x +1)
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  3. #3
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    For 1 my answer is: (-14x +16x +9)/(x^2 -5x +1)^2
    Is this Correct?
    For 2 my answer is: (2x^6 +4x^4 +6x^5 +4x +6x^3 -6x^2-6x)/(x^2 +2)^2
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  4. #4
    Junior Member plm2e's Avatar
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    what is x2 on your 2nd problem
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  5. #5
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    x^2 is the denominator because it has to be squared
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  6. #6
    Junior Member plm2e's Avatar
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    Quote Originally Posted by henri View Post
    For 1 my answer is: (-14x +16x +9)/(x^2 -5x +1)^2
    Is this Correct?
    For 2 my answer is: (2x^6 +4x^4 +6x^5 +4x +6x^3 -6x^2-6x)/(x^2 +2)^2

    I got:

    y' = [(x^2 -5x +1)(x-1) - (x^2 -x -2)(x -5)] / [x^2 -5x +1]^2

    y' = [(x^3 -6x^2 +6x -1) - (x^3 -6x^2 +3x +10)] / (x^2 -5x +1)^2

    . . . i got [3x -11] / [x^2 -5x +1]^2
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  7. #7
    Junior Member plm2e's Avatar
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    Quote Originally Posted by henri View Post
    1. f(x)=((x+1)(x-2))/(x^2 -5x +1)
    2. f(x)= (x2 − 1)(x^3 + 3x^2/x^2 + 2)

    what is x2 in
    1. f(x)= (x2 − 1)(x^3 + 3x^2/x^2 + 2)
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  8. #8
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    why is the numerator's derivative x-1 instead of 2x-1 and the same for the denominator
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  9. #9
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    Sorry for my error but the second one is (X^2 -1)(. . .)
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  10. #10
    Junior Member plm2e's Avatar
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    Quote Originally Posted by henri View Post
    why is the numerator's derivative x-1 instead of 2x-1 and the same for the denominator

    wow, you are correct, thanks, sorry to try and confuse you
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  11. #11
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    no problem thanks for all. by the way is there an easier way to put in mathematical symbols in this program? I see other posts with better formats.
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  12. #12
    Junior Member plm2e's Avatar
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    prob 2:

    i got:

    y= [x^5 +3x^4 -x^3 -3x^2] / (x^2 +2)

    y'= [(x^2 +2)(5x^4 +12x^3 -3x^2 -6x) - (x^5 +3x^4 -x^3 -3x^2)(2x)] / (x^2 +2)^2

    .....

    = [3x^6 + 6x^5 + 9x^4 + 24x^3 - 6x^2 - 12x] / (x^2 +2)^2
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  13. #13
    Junior Member plm2e's Avatar
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    not sure about the symbols. Im new to this site using it for stats help. Thought i would try one i knew how to do
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