Applicaitions of cubics + quadratics look at this :p

[dagg3r]

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 don't 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?

 

[Mulder]

#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, won't you want 5 * (9-2x)(7-2x)? Try drawing it again.

#2, which length is 'x'?