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Homework Help: Simple differentiation

  1. Oct 27, 2015 #1
    1. The problem statement, all variables and given/known data
    http://postimage.org/] Screen_Shot_2015_10_27_at_9_16_09_PM.png [/PLAIN] [Broken]
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    2. Relevant equations
    http://postimage.org/] Screen_Shot_2015_10_27_at_9_19_32_PM.png [/PLAIN] [Broken]
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    3. The attempt at a solution
    So I wanted to differentiate B(t) by saying

    B(t) = P(t)(1.05)20-t ln(1.05)

    Apparently this is the wrong answer.

    I'm supposed to change my function B(t) into this new form. From there I understand how they differentiated using the quotient rule. I can even understand how they got the new B(t) formula by splitting (1.05)20 from (1.05)-t, then changing that to 1/(1.05)t and multiplying by P(t).
    http://postimage.org/] Screen_Shot_2015_10_27_at_9_58_05_PM.png [/PLAIN] [Broken]
    image hosting sites

    What I don't understand is why my original attempt is wrong. Why is the new format necessary before we differentiate? It is because I have a negative exponent? Is it because I have two exponents?

    Thanks for the help
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Oct 27, 2015 #2


    Staff: Mentor

    B(t) is defined as a product, but it doesn't seem that you used the product rule.
    Last edited by a moderator: May 7, 2017
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