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Homework Help: Minimum and maximum of an equation

  1. Oct 24, 2008 #1
    The problem here is relatively simple...I just need to confirm something:

    A + B - C = D, in which B is a function of A and C is constant.
    dD/dA = 1 + dB/dA for the derivative
    To find a min/max of D for certain angles of A,
    dD/dA = 0 = 1 + dB/dA
    dB/dA = -1
    dB = -dA
    B = -A, which would imply that D is a min/max where B = -A and dB/dA = -1
    Dmin/max = A - A - C
    Dmin/max = -C, and thus D is a min/max where it is equivalent to -C.

    Was my mathematics wrong anywhere in there?
  2. jcsd
  3. Oct 24, 2008 #2


    Staff: Mentor

    Re: Maximum/Minimum

    If dB/dA = -1, then B = -A + a constant. IOW, the graph of B is a straight line with slope -1. Also, dD/dA = -A + a different constant.
  4. Oct 24, 2008 #3
    Re: Maximum/Minimum

    I see...thank you
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