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The surface area equation for the box below is 2x^2 + 20x.

 

 Apr 14, 2020
 #1
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Just set 2x2 + 20x = 112

 

Divide through by 2

x2 + 10x = 56

 

Rearrange

x2 + 10x - 56 = 0

 

This factors as 

(x + 14)(x - 4) = 0

 

The only positive solution is x = 4 (inches).

 Apr 14, 2020

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