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#1 2013-02-12 22:38:31

niharika_kumar
Member
From: Numeraland
Registered: 2013-02-12
Posts: 965

exponents

units digit in the number (12357)^655

please tell me the solution!!dunno


friendship is tan 90°.

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#2 2013-02-13 00:40:11

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,598

Re: exponents

Hi;

Welcome to the forum. It is a 3.

Answer is 3.

Last edited by bobbym (2013-02-13 00:47:27)


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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#3 2013-02-13 11:44:03

noelevans
Member
Registered: 2012-07-20
Posts: 236

Re: exponents

Or another way to look at it:

0th power of 12357 ends in 1.
1st power ends in 7.   2nd power ends in 9.   3rd power ends in 3.   4th power ends in 1
5th power ends in 7    6th power ends in 9    7th power ends in 3.    8th power ends in 1
9         ...            7    10      ...               9   11       ...              3    12    ...                  1, etc.

There are only four digits that occur in the powers and these repeat in the sequence 1, 7, 9, 3, 1, ...
Divide the power (655 in this case) by four and see what the remainder is.  It is three.  So the 655th
power ends in the same digit that the 3rd power does, namely 3. 

But this is a bit confusing since we get 3 for the remainder and for the last digit.
Try raising to the 656 power.  Then dividing 656 by 4 we get a remainder of zero.  So the 656
power ends in 1 same as the 0th power.

For the 654th power dividing 654 by 4 has remainder 2.  So the 654th power ends in 9 the same
as the second power.

For the 653rd power dividing 653 by 4 has remainder 1 so the units digit of the 653rd power is 7 the
same as the 1st, 5th, 9th, ... powers.

Be very blesses! smile


Writing "pretty" math (two dimensional) is easier to read and grasp than LaTex (one dimensional).
LaTex is like painting on many strips of paper and then stacking them to see what picture they make.

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#4 2013-02-13 13:12:09

cooljackiec
Member
Registered: 2012-12-13
Posts: 160

Re: exponents

is noelevans levans from AoPS?


I see you have graph paper.
You must be plotting something
lol

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#5 2013-02-13 18:21:55

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,598

Re: exponents

Hi;

I do not think so. Noel is polite.


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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#6 2013-02-15 19:53:02

niharika_kumar
Member
From: Numeraland
Registered: 2013-02-12
Posts: 965

Re: exponents

thnx guys,
epecially noel as m a student of class 9 and thus his soln ws much more easy fr me:).


friendship is tan 90°.

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#7 2013-02-17 10:49:10

noelevans
Member
Registered: 2012-07-20
Posts: 236

Re: exponents

Hi niharika_kumar,

You are quite welcome! Seeing patterns is often the name of the game in solving math problems.
And if you have access to a good math program you can often write a program to test for patterns
associated with a given problem. smile

Hi cooljackiec,  Not only am I not levans,  I have no clue as to what AoPS is.  What is it?

And thanks bobbym for the kind comment.  I do try to be polite and not hurt anyone's feelings
even if I think what they are saying is incorrect.  After all,  I have been wrong before.  As I
recall once in 1947 I was wrong about ... smile


Writing "pretty" math (two dimensional) is easier to read and grasp than LaTex (one dimensional).
LaTex is like painting on many strips of paper and then stacking them to see what picture they make.

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#8 2013-02-17 11:10:18

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,392

Re: exponents

Hi noelevans

AoPS is another forum. It's full name is Art of Problem Solving.


“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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#9 2013-02-17 11:52:30

noelevans
Member
Registered: 2012-07-20
Posts: 236

Re: exponents

Thanks stefy!

I might have worried all night about what that meant.  I'll check the site out and see what it is about.

Bless you!  smile


Writing "pretty" math (two dimensional) is easier to read and grasp than LaTex (one dimensional).
LaTex is like painting on many strips of paper and then stacking them to see what picture they make.

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#10 2013-02-17 12:02:37

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,392

Re: exponents

Hi

You're welcome (I think)!


“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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#11 2013-02-18 12:08:00

noelevans
Member
Registered: 2012-07-20
Posts: 236

Re: exponents

Yes, you do think.  And you are quite good at it! smile


Writing "pretty" math (two dimensional) is easier to read and grasp than LaTex (one dimensional).
LaTex is like painting on many strips of paper and then stacking them to see what picture they make.

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#12 2013-02-18 12:24:48

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,392

Re: exponents

Depends on what you consider good.


“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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#13 2013-02-18 13:16:04

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 84,598

Re: exponents

You think therefore you am.


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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#14 2013-02-18 13:24:19

mathgogocart
Member
Registered: 2012-04-29
Posts: 1,426

Re: exponents

bobbym wrote:

You think therefore you am.

such wise of a post.


Hey.

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