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#1 2013-07-03 02:38:12

Al-Allo
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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

#2 2013-07-03 02:40:10

bob bundy
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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

#3 2013-07-03 02:41:52

Al-Allo
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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

#4 2013-07-03 03:02:24

bobbym
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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.

#5 2013-07-03 03:03:27

Al-Allo
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Re: Little question about exponents

And why would it be that way ?

#6 2013-07-03 03:13:18

bobbym
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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.

#7 2013-07-03 03:19:25

bob bundy
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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

#8 2013-07-03 03:32:39

Al-Allo
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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 ?

#9 2013-07-03 04:02:12

bob bundy
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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

#10 2013-07-03 05:19:38

Al-Allo
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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 )

#11 2013-07-03 05:50:33

bob bundy
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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

#12 2013-07-03 06:15:53

Al-Allo
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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

#13 2013-07-03 06:23:30

bob bundy
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Re: Little question about exponents

Evaluate



Bob


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

#14 2013-07-03 07:25:00

Al-Allo
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Re: Little question about exponents

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

Last edited by Al-Allo (2013-07-03 07:25:19)

#15 2013-07-03 08:20:35

bobbym
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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.

#16 2013-07-03 08:47:31

Al-Allo
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Re: Little question about exponents



Thanks bobbym

#17 2013-07-03 08:55:19

anonimnystefy
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Re: Little question about exponents

That is correct!


The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

#18 2013-07-03 08:57:08

Al-Allo
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Re: Little question about exponents

Ah ok, thank you!

Last edited by Al-Allo (2013-07-03 08:57:21)

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