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#1 2013-07-02 04:38:12

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Little question about exponents

Hi,

If I had : 2^6/-2^5

How would I know if the base will keep it's negative sign or not ? Thanks

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#2 2013-07-02 04:40:10

bob bundy
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Registered: 2010-06-20
Posts: 6,340

Re: Little question about exponents

depends whether it says (-2)^5 or -(2^5)

Strictly, in the absence of any helpful brackets, the power takes precedence over the minus so it would be the second.

Bob


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

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#3 2013-07-02 04:41:52

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Little question about exponents

Nah, no brackets. But I'm not sure to have understood. Will there be a negative sign or not ??? And could you explain me why ? THanks

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#4 2013-07-02 05:02:24

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 85,406

Re: Little question about exponents

Hi;

bob bundy wrote:

depends whether it says (-2)^5 or -(2^5)

Without the brackets the minus sign stays.

I would think they would be asking the first one though.


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#5 2013-07-02 05:03:27

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Little question about exponents

And why would it be that way ?

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#6 2013-07-02 05:13:18

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 85,406

Re: Little question about exponents

Hi;

Because they love to be tricky.

If you assume the second alternative in Bob's suggestion you are asking where does the minus sign go in -2^5. The answer, nowhere!

But the other one (-2)^5 that illustrates a principle.


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#7 2013-07-02 05:19:25

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,340

Re: Little question about exponents

hi Al-Allo

For the rules of precedence see

http://www.mathsisfun.com/operation-order-bodmas.html

So

As it happens you would get the same result if you did (-2)^5

So here is a similar example where the denominator has an even power

Whereas


Bob


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

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#8 2013-07-02 05:32:39

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Little question about exponents

I don't think I made it clear what I wanted, the way you showed it to me bob, that I know. But I'm talking about the rules  of exponenets. ex :

2^6/-2^5 =

I know it will give me a 2^1 in my answer, but I don't know if it will stay positive or not. I could do the calculations like you did bob, but how would I know directly without doing them ?

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#9 2013-07-02 06:02:12

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,340

Re: Little question about exponents

Do you want to know how to use

but when one of the xs is replaced by -x

So it will depend on whether n is odd or even.  odd means result will be minus.  even means result will be plus.

Bob


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

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#10 2013-07-02 07:19:38

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Little question about exponents

2^6 /-1^5 * 2^5 

2^1 /-1

-2

WOuld this be correct ? (Im trying it without the brackets)

And could you show me an example where the answer would'nt be negative ? (WITHOUt brackets...thanks )

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#11 2013-07-02 07:50:33

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,340

Re: Little question about exponents

Yes, that looks ok to me.

Would you like to try some more, just to be sure?

Bob


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

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#12 2013-07-02 08:15:53

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Little question about exponents

Actually, I was able to prove to myself that without brackets my answer would always be negative, no matter what. (which was the reason why I started this topic)
But yeah, a last one, just to be sure ! thank you

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#13 2013-07-02 08:23:30

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,340

Re: Little question about exponents

Evaluate

Bob


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

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#14 2013-07-02 09:25:00

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Little question about exponents

{3^3*5^3} over {-3^2*5^2} rightarrow {-3*5} rightarrow =-15

Last edited by Al-Allo (2013-07-02 09:25:19)

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#15 2013-07-02 10:20:35

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 85,406

Re: Little question about exponents

You can use codecogs to latex that expression correctly.

http://latex.codecogs.com/editor.php


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#16 2013-07-02 10:47:31

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Little question about exponents

Thanks bobbym

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#17 2013-07-02 10:55:19

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,507

Re: Little question about exponents

That is correct!


“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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#18 2013-07-02 10:57:08

Al-Allo
Member
Registered: 2012-08-23
Posts: 293

Re: Little question about exponents

Ah ok, thank you!

Last edited by Al-Allo (2013-07-02 10:57:21)

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