Mathematics, 12.12.2019 02:31 beverlyamya

Aman wishes to construct a cylindrical barrel with a capacity of 108π ft3. the cost per square foot of the material for the side of the barrel is half that of the cost per square foot for the top and bottom. him find the dimensions of the barrel that can be constructed at a minimum cost in terms of material used.

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Answer from: bm42400

The dimensions of the barrel that makes minimum its cost of construction are

radius = 3 feet, height = 12 feet.

Step-by-step explanation:

Let r and h be the radius and height of the cylinder respectively.

Let s be the cost per square foot of the material used to construct the sides of the barrel.

The surface of the sides is the height times the perimeter of the top (or bottom) circumference:

h2πr

hence the cost to make the sides is

h2πrs

The surface of the top and bottom is two times the surface of the circumferences

$\bf 2\pi r^2$

Since the cost of the material to make the top and bottom costs double than the material for the sides, the cost to make the top and bottom is

$\bf 2s2\pi r^2 =4s\pi r^2$

The total cost to construct the barrel is then

$\bf C=h2\pi rs+4s\pi r^2$

We have that the volume of the barrel is 108π, so

$\bf \pi r^2h=108\pi$

and

$\bf h=\displaystyle\frac{108}{r^2}$

replacing this expression in the formula for the cost:

$\bf C=h2\pi rs+4s\pi r^2=\displaystyle\frac{108}{r^2}2\pi rs+4s\pi r^2=\\\\=\displaystyle\frac{216\pi s}{r}+4s\pi r^2$

Taking the derivative with respect to r:

$\bf \displaystyle\frac{dC}{dr}=-\displaystyle\frac{216\pi s}{r^2}+8s\pi r$

The critical points are the points where the derivative vanishes

$\bf \displaystyle\frac{dC}{dr}=0\Rightarrow \displaystyle\frac{216\pi s}{r^2}=8s\pi r\Rightarrow r^3=27\Rightarrow r=3\;ft$

So r = 3 is a critical point. Taking the second derivative and evaluating it in r=3 we can see it is greater than zero so r = 3 is a minimum:

$\bf \displaystyle\frac{d^2C}{dr^2}=\frac{532\pi s}{r^3}+8s\pi\Rightarrow \frac{d^2C}{dr^2}(3)0$

If r=3 ft. then h=12 ft.

We conclude that the dimensions of the barrel that makes minimum its cost of construction are:

radius = 3 feet, height = 12 feet.

Answer from: Quest

How many people are we starting with? i will answer it's just i need to divide 8 by the total amount of people to get how many tables

Answer from: Quest

x= -3 and $x=\frac{-3+/-3i\sqrt{3} }{2}$

step-by-step explanation:

to find the roots of a cubic, use division or factoring to find the factors then set equal to 0. as this is a difference of cubes, it factors into

$(x^3-a^3)=$ $(x-a)(x^2+ax+a^2)$

where a is the cube root of $a^3$ .

here this is 27 and the cube root of 27 is 3. so we write using the form:

$(x-3)(x^2+(3)x+3^2)\\(x-3)(x^2+3x+9)$ .

set each factor to 0 and solve for x.

x-3=0

x=3

the quadratic expression does not factor and must be solved using the quadratic formula.

$x=\frac{-b+/-\sqrt{b^2-4ac} }{2a}$

where a = 1, b=3, and c=9

$x=\frac{-3+/-\sqrt{3^2-4(1)(9)} }{2(1)} \\x=\frac{-3+/-\sqrt{9-36)} }{2} \\x=\frac{-3+/-\sqrt{-27)} }{2}\\x=\frac{-3+/-3i\sqrt{3} }{2}$

this cubic has two complex roots.

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Aman wishes to construct a cylindrical barrel with a capacity of 108π ft3. the cost per square foot...