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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: 6,259

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: 82,724

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.
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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#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: 82,724

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

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,259

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: 6,259

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: 6,259

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: 6,259

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: 82,724

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.
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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#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: 14,860

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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