A certain airline requires that the total outside dimensions (length + width + height) of a carry-on bag not exceed 58 inches. Suppose you want to carry on a bag whose length is twice its height. What is the largest volume bag of this shape that you can carry on a flight? (Round your answer to the nearest integer.)

Respuesta :

L+W+H=58 and L=2H, then: 2H+W+H=58 ---> 3H+W=58 or W=58-3H

Volume V=L·W·H=(2H)·(58-3H)H=116H^2-6H^3

We make its first derivative equal to 0:

232H-18H^2=0---> two solutions: H=0 (discarded) and H=232/18

Now the volumen will be: 116·(232/18)^2-6·(232/18)^3=6423 cubic inches

It is a máximum as the second derivative 232-36H is <0 for H=232/18

The volume of the bag is the amount of space in it.

The largest volume of the bag is 9366

The given parameters are:

[tex]\mathbf{l +w+h =58}[/tex]

[tex]\mathbf{l = 2h}[/tex]

Substitute [tex]\mathbf{l = 2h}[/tex] in [tex]\mathbf{l +w+h =58}[/tex]

[tex]\mathbf{2h +w+h =58}[/tex]

This gives

[tex]\mathbf{3h +w =58}[/tex]

Make w the subject

[tex]\mathbf{w =58 - 3h}[/tex]

The volume of the bag is:

[tex]\mathbf{V = lwh}[/tex]

Substitute [tex]\mathbf{l = 2h}[/tex]:

[tex]\mathbf{V = 2wh^2}[/tex]

Substitute [tex]\mathbf{w =58 - 3h}[/tex]

[tex]\mathbf{V = 2(58 - 3h)h^2}[/tex]

[tex]\mathbf{V = (116 - 6h)h^2}[/tex]

Expand

[tex]\mathbf{V = 116h^2 - 6h^3}[/tex]

Differentiate

[tex]\mathbf{V' = 232h- 18h^2}[/tex]

Set to 0

[tex]\mathbf{ 232h- 18h^2 = 0}[/tex]

Factorize

[tex]\mathbf{ h(232- 18h) = 0}[/tex]

Split

[tex]\mathbf{ h = 0\ or\ 232- 18h = 0}[/tex]

The height cannot be 0.

So, we have:

[tex]\mathbf{ 232- 18h = 0}[/tex]

This gives

[tex]\mathbf{ 18h = 232}[/tex]

Divide both sides by 18

[tex]\mathbf{ h = 13}[/tex]

Recall that: [tex]\mathbf{w =58 - 3h}[/tex]

So, we have:

[tex]\mathbf{w =58 - 3(13)}[/tex]

[tex]\mathbf{w =19}[/tex]

Substitute 19 for w in [tex]\mathbf{l = 2h}[/tex]

[tex]\mathbf{l = 2(19)}[/tex]

[tex]\mathbf{l = 38}[/tex]

Recall that: [tex]\mathbf{V = lwh}[/tex]

So, we have:

[tex]\mathbf{V = 38 \times 19 \times 13}[/tex]

[tex]\mathbf{V = 9366}[/tex]

Hence, the largest volume of the bag is 9366

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