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

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

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

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

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 104,743

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.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

Offline

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

Amazing !!!

(Thanks * 1000)

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 104,743

Hi lakeheadca;

Glad to help. Bring more!

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

Offline

Pages: **1**