Math Is Fun Forum

momofmathkid

Member

Registered: 2008-01-14

Posts: 32

Geometry Hw!

So I got this hw for over the weekend.  I did all of the problems but I got stuck on the last one! Could you please help me and show your work so that I can learn?
Thanks!

a. The formula V=4/3 (pi)r³ gives the volume of a sphere of radius r.  By solving the formula for r, show that r=(3V/4pi) 1/3 power

b. find the radius of a sphere with volume 200 cm³

c. Will the sphere in part (b) fit inside a cube with an edge that is 6cm long?

Thanks so much for the help!!

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Geometry Hw!

hi mmk

ok,so a is correct,then for b just substitute 200 cm² for V and calculate r.

for c you need to check if the diameter of a circle is smaller than the edge of the cube.

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

momofmathkid

Member

Registered: 2008-01-14

Posts: 32

Re: Geometry Hw!

thanks so much!

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Geometry Hw!

you're welcome!

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

Re: Geometry Hw!

hi momofmathkid

so times both sides by 3/4

Now divide both sides by pi

Take the cube root of both sides and swap over left and right sides so r is at the start

Now put in V = 200 to get r and double it to get the diameter.

See picture:

To fit, the diameter must be less than 6cm.

Hi Stefy

Sorry to jump in but you know me and pictures.  Just couldn't resist! 

Bob

Last edited by Bob (2011-10-01 05:32:47)

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Geometry Hw!

hi bob

it's okay.it's a free world!

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Geometry Hw!

Yes, it might be free, but no one wants to buy it anyway!

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.