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#1 2015-10-11 03:27:06
- denis_gylaev
- Member
- Registered: 2015-03-19
- Posts: 66
Hard Cone/Cylinder Problems
Find the volume of a cone that has 5 as its base radius and a lateral surface area of 65 \pi
A right circular cone and a right circular cylinder each have a radius of 4 and a height of 3. Let A and B be the lateral surface areas of the cone and cylinder, respectively. Find A/B.
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#2 2015-10-11 04:17:14
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Hard Cone/Cylinder Problems
Hi;
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.
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#3 2015-10-11 04:34:37
- denis_gylaev
- Member
- Registered: 2015-03-19
- Posts: 66
Re: Hard Cone/Cylinder Problems
Hi Bob, for number 1, I used the equation
and got 300pi initially but I saw where I went off, what did you get for number 2?Offline
#4 2015-10-11 04:50:03
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Hard Cone/Cylinder Problems
Hi;
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.
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#5 2015-10-11 04:55:10
- denis_gylaev
- Member
- Registered: 2015-03-19
- Posts: 66
Re: Hard Cone/Cylinder Problems
The lateral surface area of right circular cone is
correct?I think I might have went off on my calculations 
Last edited by denis_gylaev (2015-10-11 04:55:59)
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#6 2015-10-11 05:03:52
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Hard Cone/Cylinder Problems
That is what I used. Got it from the web...
Let me see your calculations.
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.
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#7 2015-10-11 05:16:01
- denis_gylaev
- Member
- Registered: 2015-03-19
- Posts: 66
Re: Hard Cone/Cylinder Problems
Ok, I redid my calculations and got the same answer as you. Here is my work:
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#8 2015-10-11 05:19:10
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Hard Cone/Cylinder Problems
Ok, I redid my calculations and got the same answer as you.
Someday, in the not so distant future, I envision a world where everyone, everywhere, gets the same answers as I do.
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.
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#9 2015-10-11 05:41:14
- denis_gylaev
- Member
- Registered: 2015-03-19
- Posts: 66
Re: Hard Cone/Cylinder Problems
A plane intersects a sphere, forming a circle that has area
. If this plane is 5 units from the center of the sphere, then what is the surface area of the sphere?I got 232pi but that seems very, very wrong...
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#10 2015-10-16 01:42:19
- Bob
- Administrator
- Registered: 2010-06-20
- Posts: 10,621
Re: Hard Cone/Cylinder Problems
hi denis_gylaev
I've been away so only just read this. I get a smaller answer. Try this:
Work out the radius of the circle. (leave with a square root as it simplifies anyway later)
From the centre of the sphere to the centre of the circle and then out to the edge of the circle makes a right angled triangle. So use Pythagoras to get the radius of the sphere.
Bob
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 
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