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Thread: pre cal questions... soo confused

  1. #1
    Sep 2008

    pre cal questions... soo confused

    Ok there are three questions from my precal homework that i CANNOT figure out. its driving me nuts. Any help?

    Suppose that the manufacturer of a gas clothes dryer has found that, when the unit price is p dollars, the revenue R (in dollars) is given by the equation below.
    R(p) = -4p2 + 2480p
    What unit price for the dryer should be established to maximize revenue?
    What is the maximum revenue?
    David has available 550 yards of fencing and wishes to enclose a rectangular area.
    (a) Express the area A of the rectangle as a function of the width x of the rectangle.
    A(x) =

    (b) For what value of x is the area largest?
    x =

    (c) What is the maximum area?
    square yards

    A farmer with 4000 meters of fencing wants to enclose a rectangular plot that borders on a river. If the farmer does not fence the side along the river, what is the largest area that can be enclosed?
    square meters
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  2. #2
    Oct 2007
    It would have been nice if you actually typed the equations and the problems so the people who are helping you doesn't have to read as hard. Also make one thread per problem.

    $\displaystyle R(p)= -4p^2+2480p $

    This is a upside down parabola.
    At where is the highest point of upside parabola and how do you find it?
    This point [p,R(p)] will give you the answer you want for number 1.

    Number 2

    so the perimeter of a rectangle is
    $\displaystyle P=2(l+w) $
    you know that $\displaystyle 550= 2 (l+w) $
    Since it wants the width to be x
    $\displaystyle 225-w=l $
    $\displaystyle A= lw $
    $\displaystyle A(w)=w(225-w) $

    This is also a upside down parabola. You should know how to do the rest.
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