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D/ds s/sqrt(60s + 25)

  1. Oct 26, 2011 #1
    1. The problem statement, all variables and given/known data

    d/ds s/sqrt(60s + 25)

    2. Relevant equations



    3. The attempt at a solution

    d/ds s/sqrt(60s + 25) = d/ds s(60s + 25)^-1/2
    if a = s(60s + 25)^-1/2
    and b = (60s + 25)
    da/db = -1/2s(60s +25)^-3/2
    db/ds = 60
    da/ds = -30s(60s +25)^-3/2

    Any help much appreciated.
     
  2. jcsd
  3. Oct 26, 2011 #2

    CompuChip

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    Science Advisor
    Homework Helper

    It looks like you are trying to use the chain rule, but that doesn't quite work here. The reason is that if you want to calculate da/db, you have to write a completely in terms of b, i.e. as (b - 25) / 60 * b-1/2.

    Note that after the rewriting in your first line (s (60s + 25)-1/2) you have a product of two functions, i.e. you are looking for d/ds(a b) with a = s, b = (60s + 25)-1/2
     
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