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April 19, 2014

April 19, 2014

Posted by **Firdous** on Monday, April 29, 2013 at 5:43am.

From each of its corner a square piece 2 units on a side is cut out.The flaps are then turned up to form an open box that has a volume of 70 cubic units.Find the length and width of the original piece of cardboard.

- algebra -
**Reiny**, Monday, April 29, 2013 at 9:51amDid you make a sketch?

width of cardboard --- x

length of cardboard -- x+2

width of box = x-4

length of box = x-2

height of box = x

volume = x(x-2)(x-4) = 70

x^3 - 6x^2 + 8x - 70 = 0

That was easy so far, but now we have a nasty cubic.

I tried factors of 70 , no luck

so I used Wolfram to find

x = appr 6.4442

original widht = 6.442

original length = 8.442

http://www.wolframalpha.com/input/?i=x%5E3+-+6x%5E2+%2B+8x+-+70+%3D+0

check:

original widht = 6.442

original length = 8.442

box base is 2.4442 by 4.4442

volume = 2.4442 x 4.4442 x 6.4442 = 70.00002 , not bad

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