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

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**RadioBoy****Member**- Registered: 2012-12-19
- Posts: 1

Hello, I have just joined the math is fun forum. I expect interesting things here and will also share my experience of math. For example, the miracle of digit 9. The product of digit nine in interaction with itself will always be nine (9 x 9 = 18 = 1+8 =9).

If you are thinking of switching or using alternative energy in your home, solar power is the best choice that can sustain your lifestyle.

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

Hi RadioBoy

Welcone to the forum!

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.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,856

Hi RadioBoy;

Welcome to the forum.

**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.**

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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 20,357

Hi RadioBoy,

**Welcome to the forum!**

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,608

Welcome!

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**mathaholic****Member**- From: Earth
- Registered: 2012-11-29
- Posts: 3,246

Belated welcome to the forum, RadioBoy!

Mathaholic | 10th most active poster | Maker of the 350,000th post | Person | rrr's classmate

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,525

hi RadioBoy,

**Welcome to the forum.**

For example, the miracle of digit 9. The product of digit nine in interaction with itself will always be nine (9 x 9 = 18 = 1+8 =9).

or a number that reduces to nine eg. 109739369 x 9 = 987654321 ....9+8+7+6+5+4+3+2+1= 45 ... 4+5 = 9.

So here's a challenge:

Why does this happen?

Why doesn't it happen for, say, 7?

What other numbers does it happen for?

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

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