Ribbon cost $1.44 for 3 m what is the cost per metre?

A metal cylinder can with an open top and closed bottom is to have volume 4 cubic feet. Approximate the dimensions that require

Aleksandr-060686 [28]

Answer:

$r\approx 1.084\ feet$

$h\approx 1.084\ feet$

$\displaystyle A=11.07\ ft^2$

Step-by-step explanation:

<u>Optimizing With Derivatives </u>

The procedure to optimize a function (find its maximum or minimum) consists in :

Produce a function which depends on only one variable
Compute the first derivative and set it equal to 0
Find the values for the variable, called critical points
Compute the second derivative
Evaluate the second derivative in the critical points. If it results positive, the critical point is a minimum, if it's negative, the critical point is a maximum

We know a cylinder has a volume of 4 $ft^3$ . The volume of a cylinder is given by

$\displaystyle V=\pi r^2h$

Equating it to 4

$\displaystyle \pi r^2h=4$

Let's solve for h

$\displaystyle h=\frac{4}{\pi r^2}$

A cylinder with an open-top has only one circle as the shape of the lid and has a lateral area computed as a rectangle of height h and base equal to the length of a circle. Thus, the total area of the material to make the cylinder is

$\displaystyle A=\pi r^2+2\pi rh$

Replacing the formula of h

$\displaystyle A=\pi r^2+2\pi r \left (\frac{4}{\pi r^2}\right )$

Simplifying

$\displaystyle A=\pi r^2+\frac{8}{r}$

We have the function of the area in terms of one variable. Now we compute the first derivative and equal it to zero

$\displaystyle A'=2\pi r-\frac{8}{r^2}=0$

Rearranging

$\displaystyle 2\pi r=\frac{8}{r^2}$

Solving for r

$\displaystyle r^3=\frac{4}{\pi }$

$\displaystyle r=\sqrt[3]{\frac{4}{\pi }}\approx 1.084\ feet$

Computing h

$\displaystyle h=\frac{4}{\pi \ r^2}\approx 1.084\ feet$

We can see the height and the radius are of the same size. We check if the critical point is a maximum or a minimum by computing the second derivative

$\displaystyle A''=2\pi+\frac{16}{r^3}$

We can see it will be always positive regardless of the value of r (assumed positive too), so the critical point is a minimum.

The minimum area is

$\displaystyle A=\pi(1.084)^2+\frac{8}{1.084}$

$\boxed{ A=11.07\ ft^2}$

8 0

2 years ago

the sponsor of a concert promises the concert singer a fee based on $5 per person in the audience. if attendence is below 200, h

larisa86 [58]

This would help you alot.

3 0

3 years ago

Read 2 more answers

A person that is 5 feet tall casts a shadow 25 feet long. How long is the shadow of a tree that is 15 feet tall?

fiasKO [112]

The person and his shadow make a right triangle as well as the tree and it's shadow. they will be similar right triangles containing angles that are equal. I'm in similar triangles the angles are proportional so a ratio could be used to determine the shadow length. this ratio is:
25/5 = x/15
(Notice that both the height of the person and
the height of the tree height of the tree are on
the bottom because these would be similar
sides and the same for the shadows with both
on top. this could easily have been switched
with the shadows on bottom and heights on
top like:
5/25 = 15/x
however I noticed the 25/5 could easily be
reduced. this eliminated the need for cross
multiplication.)

The 25/5 can be reduced to 5:
5 = x/15
and then multiply both sides by 15 and you get:
x = 75
so the answer is 75 feet long.

this can be checked various ways. using trigonometry we have the opposite and adjacent sides so tangent could be used to find the angle between the shadow and the hypotenuse. this is:
tan (x) = opposite/adjacent
opposite = height
adjacent = shadow
so:
tan (x) = 5/25 for person
tan (x) = 15/75 for tree
these equations both reduce to:
tan (x) = 1/5
And of both equations are the same then the angLee are equal creating similar triangles and a correct answer

4 0

3 years ago

If you can please do it all just tryna go to sleep

Lubov Fominskaja [6]

Answer:

1. 1

2. -3

3. yes

4. no, it is not, because the function stop at point (-6, -2)

5. -2

6 0

2 years ago

W^2-8w-20 factor the polynomial.

Mademuasel [1]

Your answer would be (w+2)(w−10). If you want me to explain please don't hesitate to ask.

6 0

3 years ago

Read 2 more answers