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Precalculus

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A builder has 600 feet of fencing to enclose three adjacent rectangular partioned areas. Find the largest possible enclosed area of the partioned areas.

  • Precalculus -

    I will assume the maximum area is achieved with three adjacent rectangular areas with total length (end to end) = y and width = x.

    Total area = x * y
    2y + 3x = 600

    A = x * (300 - 1.5 x) = 300 x -1.5 x^2
    dA/dx = 0
    300 = 3x
    x = 100
    y = (600 - 300)/2 = 150
    Total area = x*y = 15,000

  • Precalculus (correction) -

    I just realized that the equation that relates x and y to the total length of material should be
    2y + 4x = 600.
    You need 4 fence segments of length x to create 3 areas.
    Therefore, y = 300 - 2x
    A = x*(300 - 2x) = 300x - 2x^2
    Since dA/dx = 0,
    4x = 300 and x = 75.
    y = 150

    Maximum total area = x*y = 11,250

    You say you are takng a precalculus course, but I have used calculus in this derivation.

    The same result can be obtained by "completing the square" with the A(x) function.

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