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

You are not logged in.

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

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.

Offline

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

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### 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.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Offline

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

Member
Registered: 2010-01-31
Posts: 37

Amazing !!!
(Thanks * 1000)

Offline

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

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606