Math Is Fun Forum
  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

#1 2010-06-19 03:49:58

lakeheadca
Member
Registered: 2010-01-31
Posts: 37

Find diameter

how to find the diameter of the given figure.
thank you so much guys, specially bobby who always help so fast. He is great.

View Image: cone.GIF

Offline

#2 2010-06-19 05:45:06

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 82,672

Re: Find diameter

specially bobby who always help so fast. He is great.

Yea, he is, when I grow up I want to be him.

We need to find r of the small circle. Fortunately there is a relationship that does all the work. There is an easier one that relates r to the heights but I am too lazy to look for it.

Where B1 is the area of the smaller circle. B2 is the area of the larger circle. h1 = height from the apex to smaller circle and h2 to the larger.

Do you see that it contains the little r we need. Like magic.

Cross multiply:

Divide both sides by pi.

Divide both sides by 144:

r = 6 and r = -6

Can't have a radius of - 6 so r = 6 and d = 2r = 12.

diameter of smaller circle is 12


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Online

#3 2010-06-20 05:05:14

lakeheadca
Member
Registered: 2010-01-31
Posts: 37

Re: Find diameter

Amazing !!!
(Thanks * 1000)

Offline

#4 2010-06-20 05:12:30

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 82,672

Re: Find diameter

Hi lakeheadca;

Glad to help. Bring more!


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

Online

Board footer

Powered by FluxBB