Answer:
Dimensions are 2 m by 1 meter by 1 meter,
Minimum cost is $ 18.
Step-by-step explanation:
Let w be the width ( in meters ) of the container,
Since, the length is twice of the width,
So, length of the container = 2w,
Now, if h be the height of the container,
Volume = length × width × height
2 = 2w × w × h
1 = w² × h
![\implies h=\frac{1}{w^2}](https://tex.z-dn.net/?f=%5Cimplies%20h%3D%5Cfrac%7B1%7D%7Bw%5E2%7D)
Since, the area of the base = l × w = 2w × w = 2w²,
Area of the lid = l × w = 2w²,
While the area of the sides = 2hw + 2hl
= 2h( w + l)
![= 2\times \frac{1}{w^2}(w+2w)](https://tex.z-dn.net/?f=%3D%202%5Ctimes%20%5Cfrac%7B1%7D%7Bw%5E2%7D%28w%2B2w%29)
![=\frac{6w}{w^2}](https://tex.z-dn.net/?f=%3D%5Cfrac%7B6w%7D%7Bw%5E2%7D)
Since, Material for the base costs $1 per m². Material for the sides and lid costs $2 per m²,
So, the total cost,
![C(w) = 1\times 2w^2+2\times 2w^2 + 2\times \frac{6}{w}](https://tex.z-dn.net/?f=C%28w%29%20%3D%201%5Ctimes%202w%5E2%2B2%5Ctimes%202w%5E2%20%2B%202%5Ctimes%20%5Cfrac%7B6%7D%7Bw%7D)
![=2w^2+4w^2+\frac{12}{w}](https://tex.z-dn.net/?f=%3D2w%5E2%2B4w%5E2%2B%5Cfrac%7B12%7D%7Bw%7D)
![=6w^2+\frac{12}{w}](https://tex.z-dn.net/?f=%3D6w%5E2%2B%5Cfrac%7B12%7D%7Bw%7D)
Differentiating with respect to w,
![C'(w) = 12w -\frac{12}{w^2}](https://tex.z-dn.net/?f=C%27%28w%29%20%3D%2012w%20-%5Cfrac%7B12%7D%7Bw%5E2%7D)
Again differentiating with respect to w,
![C''(w) = 12 + \frac{24}{w^3}](https://tex.z-dn.net/?f=C%27%27%28w%29%20%3D%2012%20%2B%20%5Cfrac%7B24%7D%7Bw%5E3%7D)
For maxima or minima,
C'(w) = 0
![\implies 12w -\frac{12}{w^2}=0](https://tex.z-dn.net/?f=%5Cimplies%2012w%20-%5Cfrac%7B12%7D%7Bw%5E2%7D%3D0)
![\implies 12w^3 - 12=0](https://tex.z-dn.net/?f=%5Cimplies%2012w%5E3%20-%2012%3D0)
![w^3-1=0\implies w = 1](https://tex.z-dn.net/?f=w%5E3-1%3D0%5Cimplies%20w%20%3D%201)
For w = 1, C''(w) = positive,
Hence, for width 1 m the cost is minimum,
Therefore, the minimum cost is C(1) = 6(1)²+12 = $ 18,
And, the dimension for which the cost is minimum is,
2 m by 1 meter by 1 meter.