Answer:
radius r = 3.414 in
height h = 6.8275 in
Step-by-step explanation:
From the information given:
The volume V of a closed cylindrical container with its surface area can be expressed as follows:
[tex]V = \pi r^2 h[/tex]
[tex]S = 2 \pi rh + 2 \pi r^2[/tex]
Given that Volume V = 250 in²
Then;
[tex]\pi r^2h = 250 \\ \\ h = \dfrac{250}{\pi r^2}[/tex]
We also know that the cylinder contains top and bottom circle and the area is equal to πr²,
Hence, if we incorporate these areas in the total area of the cylinder.
Then;
[tex]S = 2\pi r h + 2 \pi r ^2[/tex]
[tex]S = 2\pi r (\dfrac{250}{\pi r^2}) + 2 \pi r ^2[/tex]
[tex]S = \dfrac{500}{r} + 2 \pi r ^2[/tex]
To find the minimum by determining the radius at which the surface by using the first-order derivative.
[tex]S' = 0[/tex]
[tex]- \dfrac{500}{r^2} + 4 \pi r = 0[/tex]
[tex]r^3 = \dfrac{500 }{4 \pi}[/tex]
[tex]r^3 = 39.789[/tex]
[tex]r =\sqrt[3]{39.789}[/tex]
r = 3.414 in
Using the second-order derivative of S to determine the area is maximum or minimum at the radius, we have:
[tex]S'' = - \dfrac{500(-2)}{r^3}+ 4 \pi[/tex]
[tex]S'' = \dfrac{1000}{r^3}+ 4 \pi[/tex]
Thus, the minimum surface area will be used because the second-derivative shows that the area function is higher than zero.
Thus, from [tex]h = \dfrac{250}{\pi r^2}[/tex]
[tex]h = \dfrac{250}{\pi (3.414) ^2}[/tex]
h = 6.8275 in
