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Mathematica partial differentiation weirdness

  1. Feb 19, 2012 #1
    I am checking my homework with mathematica, but sometimes when I write stuff like
    D[(x/((x^2 - y^2)^0.5)), y] , which is supposed to give me the partial derivative of x/((x^2 - y^2)^0.5) with respect to y, i get answer like:

    (1. x y)/(x^2 - y^2)^1.5

    which is right, except for the random "1."

    as another example, when I differentiate above function with respect to x, I again get an answer with "1.x^2" in a numerator.

    what on earth is this "1." ?
     
  2. jcsd
  3. Feb 19, 2012 #2

    lurflurf

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    Homework Helper

    1x=x

    In this case the 1. means that the answer is approximate, as your .5 is approximate.

    D[(x/((x^2 - y^2)^a)), y] =(2a x y)/(x^2 - y^2)^(a+1)

    if a=1/2
    2a=1
    a+1=1.5

    if it is only approximately true
    a=.5
    2a=1.
    1+a=1.5
     
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