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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: The Foundation
- Registered: 2011-05-23
- Posts: 14,801

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

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 81,367

Hi RadioBoy;

Welcome to the forum.

**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.**

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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 12,919

Hi RadioBoy,

**Welcome to the forum!**

Character is who you are when no one is looking.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,529

Welcome!

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

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**mathaholic****Member**- From: Juliania
- Registered: 2012-11-29
- Posts: 2,797
- Website

Belated welcome to the forum, RadioBoy!

"Double the fun, double the thrill, double the coolness" - Julianthewiki

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,092

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

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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