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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: 15,937

Hi RadioBoy

Welcone to the forum!

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: 97,123

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.**

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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 17,484

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: 7,569

Welcome!

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**mathaholic****Member**- From: Earth
- Registered: 2012-11-29
- Posts: 3,020

Belated welcome to the forum, RadioBoy!

Mathaholic | 17th most active poster | 681st most recent person to join MIFF | Person | rrr's classmate

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,182

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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