Answer:
1)
, 2) The domain of S is
. The range of S is
, 3)
, 4)
, 5) ![S = 164.830\,in^{2}](https://tex.z-dn.net/?f=S%20%3D%20164.830%5C%2Cin%5E%7B2%7D)
Step-by-step explanation:
1) The function of the box is:
![S = 2\cdot (w - 2\cdot x)\cdot x + 2\cdot (l-2\cdot x)\cdot x +(w-2\cdot x)\cdot (l-2\cdot x)](https://tex.z-dn.net/?f=S%20%3D%202%5Ccdot%20%28w%20-%202%5Ccdot%20x%29%5Ccdot%20x%20%2B%202%5Ccdot%20%28l-2%5Ccdot%20x%29%5Ccdot%20x%20%2B%28w-2%5Ccdot%20x%29%5Ccdot%20%28l-2%5Ccdot%20x%29)
![S = 2\cdot w\cdot x - 4\cdot x^{2} + 2\cdot l\cdot x - 4\cdot x^{2} + w\cdot l -2\cdot (l + w)\cdot x + l\cdot w](https://tex.z-dn.net/?f=S%20%3D%202%5Ccdot%20w%5Ccdot%20x%20-%204%5Ccdot%20x%5E%7B2%7D%20%2B%202%5Ccdot%20l%5Ccdot%20x%20-%204%5Ccdot%20x%5E%7B2%7D%20%2B%20w%5Ccdot%20l%20-2%5Ccdot%20%28l%20%2B%20w%29%5Ccdot%20x%20%2B%20l%5Ccdot%20w)
![S = 2\cdot (w+l)\cdot x - 8\cdpt x^{2} + 2\cdot w \cdot l - 2\cdot (l+w)\cdot x](https://tex.z-dn.net/?f=S%20%3D%202%5Ccdot%20%28w%2Bl%29%5Ccdot%20x%20-%208%5Ccdpt%20x%5E%7B2%7D%20%2B%202%5Ccdot%20w%20%5Ccdot%20l%20-%202%5Ccdot%20%28l%2Bw%29%5Ccdot%20x)
![S = 2\cdot w\cdot l - 8\cdot x^{2}](https://tex.z-dn.net/?f=S%20%3D%202%5Ccdot%20w%5Ccdot%20l%20-%208%5Ccdot%20x%5E%7B2%7D)
2) The maximum cutout is:
![2\cdot w \cdot l - 8\cdot x^{2} = 0](https://tex.z-dn.net/?f=2%5Ccdot%20w%20%5Ccdot%20l%20-%208%5Ccdot%20x%5E%7B2%7D%20%3D%200)
![w\cdot l - 4\cdot x^{2} = 0](https://tex.z-dn.net/?f=w%5Ccdot%20l%20-%204%5Ccdot%20x%5E%7B2%7D%20%3D%200)
![4\cdot x^{2} = w\cdot l](https://tex.z-dn.net/?f=4%5Ccdot%20x%5E%7B2%7D%20%3D%20w%5Ccdot%20l)
![x = \frac{\sqrt{w\cdot l}}{2}](https://tex.z-dn.net/?f=x%20%3D%20%5Cfrac%7B%5Csqrt%7Bw%5Ccdot%20l%7D%7D%7B2%7D)
The domain of S is
. The range of S is ![0 \leq S \leq 2\cdot w \cdot l](https://tex.z-dn.net/?f=0%20%5Cleq%20S%20%5Cleq%202%5Ccdot%20w%20%5Ccdot%20l)
3) The surface area when a 1'' x 1'' square is cut out is:
![S = 2\cdot (8\,in)\cdot (11.5\,in)-8\cdot (1\,in)^{2}](https://tex.z-dn.net/?f=S%20%3D%202%5Ccdot%20%288%5C%2Cin%29%5Ccdot%20%2811.5%5C%2Cin%29-8%5Ccdot%20%281%5C%2Cin%29%5E%7B2%7D)
![S = 176\,in^{2}](https://tex.z-dn.net/?f=S%20%3D%20176%5C%2Cin%5E%7B2%7D)
4) The size is found by solving the following second-order polynomial:
![20\,in^{2} = 2 \cdot (8\,in)\cdot (11.5\,in)-8\cdot x^{2}](https://tex.z-dn.net/?f=20%5C%2Cin%5E%7B2%7D%20%3D%202%20%5Ccdot%20%288%5C%2Cin%29%5Ccdot%20%2811.5%5C%2Cin%29-8%5Ccdot%20x%5E%7B2%7D)
![20\,in^{2} = 184\,in^{2} - 8\cdot x^{2}](https://tex.z-dn.net/?f=20%5C%2Cin%5E%7B2%7D%20%3D%20184%5C%2Cin%5E%7B2%7D%20-%208%5Ccdot%20x%5E%7B2%7D)
![8\cdot x^{2} - 164\,in^{2} = 0](https://tex.z-dn.net/?f=8%5Ccdot%20x%5E%7B2%7D%20-%20164%5C%2Cin%5E%7B2%7D%20%3D%200)
![x \approx 4.528\,in](https://tex.z-dn.net/?f=x%20%5Capprox%204.528%5C%2Cin)
5) The equation of the box volume is:
![V = (w-2\cdot x)\cdot (l-2\cdot x) \cdot x](https://tex.z-dn.net/?f=V%20%3D%20%28w-2%5Ccdot%20x%29%5Ccdot%20%28l-2%5Ccdot%20x%29%20%5Ccdot%20x)
![V = [w\cdot l -2\cdot (w+l)\cdot x + 4\cdot x^{2}]\cdot x](https://tex.z-dn.net/?f=V%20%3D%20%5Bw%5Ccdot%20l%20-2%5Ccdot%20%28w%2Bl%29%5Ccdot%20x%20%2B%204%5Ccdot%20x%5E%7B2%7D%5D%5Ccdot%20x)
![V = w\cdot l \cdot x - 2\cdot (w+l)\cdot x^{2} + 4\cdot x^{3}](https://tex.z-dn.net/?f=V%20%3D%20w%5Ccdot%20l%20%5Ccdot%20x%20-%202%5Ccdot%20%28w%2Bl%29%5Ccdot%20x%5E%7B2%7D%20%2B%204%5Ccdot%20x%5E%7B3%7D)
![V = (8\,in)\cdot (11.5\,in)\cdot x - 2\cdot (19.5\,in)\cdot x^{2} + 4\cdot x^{3}](https://tex.z-dn.net/?f=V%20%3D%20%288%5C%2Cin%29%5Ccdot%20%2811.5%5C%2Cin%29%5Ccdot%20x%20-%202%5Ccdot%20%2819.5%5C%2Cin%29%5Ccdot%20x%5E%7B2%7D%20%2B%204%5Ccdot%20x%5E%7B3%7D)
![V = (92\,in^{2})\cdot x - (39\,in)\cdot x^{2} + 4\cdot x^{3}](https://tex.z-dn.net/?f=V%20%3D%20%2892%5C%2Cin%5E%7B2%7D%29%5Ccdot%20x%20-%20%2839%5C%2Cin%29%5Ccdot%20x%5E%7B2%7D%20%2B%204%5Ccdot%20x%5E%7B3%7D)
The first derivative of the function is:
![V' = 92\,in^{2} - (78\,in)\cdot x + 12\cdot x^{2}](https://tex.z-dn.net/?f=V%27%20%3D%2092%5C%2Cin%5E%7B2%7D%20-%20%2878%5C%2Cin%29%5Ccdot%20x%20%2B%2012%5Ccdot%20x%5E%7B2%7D)
The critical points are determined by equalizing the derivative to zero:
![12\cdot x^{2}-(78\,in)\cdot x + 92\,in^{2} = 0](https://tex.z-dn.net/?f=12%5Ccdot%20x%5E%7B2%7D-%2878%5C%2Cin%29%5Ccdot%20x%20%2B%2092%5C%2Cin%5E%7B2%7D%20%3D%200)
![x_{1} \approx 4.952\,in](https://tex.z-dn.net/?f=x_%7B1%7D%20%5Capprox%204.952%5C%2Cin)
![x_{2}\approx 1.548\,in](https://tex.z-dn.net/?f=x_%7B2%7D%5Capprox%201.548%5C%2Cin)
The second derivative is found afterwards:
![V'' = 24\cdot x - 78\,in](https://tex.z-dn.net/?f=V%27%27%20%3D%2024%5Ccdot%20x%20-%2078%5C%2Cin)
After evaluating each critical point, it follows that
is an absolute minimum and
is an absolute maximum. Hence, the value of the cutoff so that volume is maximized is:
![x \approx 1.548\,in](https://tex.z-dn.net/?f=x%20%5Capprox%201.548%5C%2Cin)
The surface area of the box is:
![S = 2\cdot (8\,in)\cdot (11.5\,in)-8\cdot (1.548\,in)^{2}](https://tex.z-dn.net/?f=S%20%3D%202%5Ccdot%20%288%5C%2Cin%29%5Ccdot%20%2811.5%5C%2Cin%29-8%5Ccdot%20%281.548%5C%2Cin%29%5E%7B2%7D)
![S = 164.830\,in^{2}](https://tex.z-dn.net/?f=S%20%3D%20164.830%5C%2Cin%5E%7B2%7D)