View Full Version : Word Problem for Linear-Quadratic Systems

Lyphta

11-09-2005, 06:28 PM

A square cupboard door contains four square panels. The border around each square panel has a uniform width of 4 cm. if the total area of the door excluding the panels is 720 cm^2, what are the dimensions of the door and each panel.

use substitution

stapel

11-09-2005, 06:36 PM

How far have you gotten? You've drawn the picture and... then what?

Please reply with specifics. Thank you.

Eliz.

Lyphta

11-09-2005, 06:43 PM

well the picture looks something like this:

http://img85.imageshack.us/img85/4122/mathprob8ui.png (http://imageshack.us)

and then i was thinking that one of the equations was x^2=720. but i think thats wrong. and i havent figured out the second one yet. cause i made the boxes inside equal to y and if each border was 4 cm i was thinking it would be 16...

stapel

11-09-2005, 06:47 PM

What does "x" stand for? Or "y"?

Please include units in your description. Thank you.

Eliz.

Lyphta

11-09-2005, 06:55 PM

oh yeah. i put my X= to one of the sides on the big square. and my Y=to one of the sides in the smaller square.

stapel

11-09-2005, 11:14 PM

Thank you for the clarification (and my apologies for the delay in my reply, but I only just now got back home).

If the length of the side of an interior (and square) panel is "y", then the area of one panel is y<sup>2</sup> and the area of all four panels is 4y<sup>2</sup>.

Looking at the graph, the width of the door is 4 + y + 4 + y + 4 = 2y + 12. So is the height. So what is the area?

Now subtract the panel area from the total area, set equal to the given "door less panels" area, and solve.

I don't know what they mean by "use substitution". Sorry.

Eliz.

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