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Simple Derivative Question

  1. May 30, 2012 #1
    I am having trouble with this derivation: f(q)=q(Q-q). We want to find the values that maximize the vaule of q so the book sets the derivative equal to 0 and gets Q-2q=0

    When I try to do the derivative of f(q)=q(Q-q), I used the product rule

    1(Q-q) + q(Q-1)=0
    Q-q+Qq-q=0
    Q+Qq-2q=0

    I have an extra (Qq) I don't know how to get rid of.
     
  2. jcsd
  3. May 30, 2012 #2

    Mark44

    Staff: Mentor

    There's a mistake above. d/dq(Q - q) = -1, not Q - 1. Q is a constant in this function.
     
  4. May 30, 2012 #3
    ah, too many q's running around. Thank you
     
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