Answer:
[tex]1.91\ \text{in}[/tex]
[tex]3.84\ \text{in}[/tex]
Step-by-step explanation:
V = Volume of cylinder = [tex]44\ \text{in}^3[/tex]
h = Height of cylinder
r = Radius of cylinder
Volume of cylinder is given by
[tex]V=\pi r^2h\\\Rightarrow h=\dfrac{V}{\pi r^2}\\\Rightarrow h=\dfrac{44}{\pi r^2}[/tex]
Total surface area of a cylinder is given by
[tex]S=2\pi r^2+2\pi rh\\\Rightarrow S=2\pi r^2+2\pi r\times\dfrac{44}{\pi r^2}\\\Rightarrow S=2\pi r^2+\dfrac{88}{r}[/tex]
Differentiating with respect to radius
[tex]\dfrac{dS}{dr}=4\pi r-\dfrac{88}{r^2}[/tex]
Equating with zero
[tex]4\pi r-\dfrac{88}{r^2}=0\\\Rightarrow 4\pi r=\dfrac{88}{r^2}\\\Rightarrow r^3=\dfrac{88}{4\pi}\\\Rightarrow r=(\dfrac{22}{\pi})^{\dfrac{1}{3}}\\\Rightarrow r=1.91\ \text{in}[/tex]
Double derivative of S
[tex]\dfrac{d^2S}{dr^2}=4\pi+176>0[/tex]
So [tex]r[/tex] is minimum at [tex]\dfrac{dS}{dr}=0[/tex]
[tex]h=\dfrac{44}{\pi r^2}=\dfrac{44}{\pi 1.91^2}\\\Rightarrow h=3.84\ \text{in}[/tex]
So the radius and height of the cylinder is [tex]1.91\ \text{in}[/tex] and [tex]3.84\ \text{in}[/tex] respectively such that the least amount of metal is used.
