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Homework Help: Finding the Derivative

  1. Feb 14, 2009 #1
    1. The problem statement, all variables and given/known data
    Find ds/dt for s=(t2)(1/7)


    2. Relevant equations
    I attempted to find the answer by using the chain rule...


    3. The attempt at a solution
    ds/dt = (1/7)*(t2)-(6/7)*(2t)
    ds/dt = (2/7)*t*(t2)-(6/7)

    I belive that would be the answer but the problem is that the answer key in the book tells me that ds/dt = (2/7)t-(5/7)

    I don't understand what they did to cancel out the t2 ang get the power to be -5/7
     
  2. jcsd
  3. Feb 14, 2009 #2
    Simplify 's' first before you take the derivative. Remember the properties of exponents.
     
  4. Feb 14, 2009 #3
    thanks i got it now that i said s=t(2/7)
     
  5. Feb 14, 2009 #4

    Mark44

    Staff: Mentor

    Your answer is correct, but it's not as simplified as it can be. Also, using the chain rule led to a lot of unnecessary work that could have been avoided by simplifying the expression first.

    (2/7)*t*(t2)-(6/7)
    =(2/7) *t* t-12/7
    =(2/7) *t7/7* t-12/7
    = (2/7) * t-5/7

     
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