Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Applicaitions of cubics + quadratics look at this :p

  1. May 12, 2003 #1
    1. A student wants to construct an open box with a base area 35 cm2 from a rectangular piece of cardboard measuring 9 cm by 7 cm.
    Find x, where x cm is the length of the side of the square which must be removed from each corner of the cardboard.

    this is what i did, i went (9-2x)*(7-2x)=35, then i get it in a form of a quad or cubic, then find the x-intercepts?

    2. From a rectangular sheet of metal, ABCD, the part ABP is cut, and the area of the remaining part is 114 cm2.
    Find the value of x.

    i am totally lost i dont know what to do here

    3. The demand, x units of a certain product is given by x = 400 - 0.25p per month
    where p is the selling price per unit. The cost, $C, to produce x units is given by
    C = 9600 + 1200x
    a) Express p in terms of x.

    yeah this one i did. p=4 (400 - x)

    b) The revenue obtained is a result of selling a number of units at a certain price.
    Express the revenue, R, in terms of x.

    totally lost, do i just use the x= 400 - 0.25p , and sub p from previous example in?

    d) Determine the number of units that must be produced and sold each month :

    i) in order to break even

    i have to use the c= formula and find the x-intercepts?

    ii) if the profit is to be $300 per month.

    totally lost here

    c) Express the profit, P, in terms of x.

    profit... how do i do that?
  2. jcsd
  3. May 12, 2003 #2
    #1 - is there anything that says you have to cut out squares? You can cut out rectangles and still form a box, so you want x and y, say.

    edit; ok if it does have to eb squares, wont you want 5 * (9-2x)(7-2x)? Try drawing it again.

    #2, which length is 'x'?
    Last edited: May 12, 2003
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook