Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

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

Hi,

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

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

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,308

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

Offline

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

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

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 84,512

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.**

Offline

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

And why would it be that way ?

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 84,512

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.**

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,308

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

Offline

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

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 ?

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,308

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

Offline

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

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 )

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,308

Yes, that looks ok to me.

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

Bob

Offline

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

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

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,308

Evaluate

Bob

Offline

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

{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)*

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 84,512

You can use codecogs to latex that expression correctly.

**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.**

Offline

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

Thanks bobbym

Offline

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,375

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

**Online**

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

Ah ok, thank you!

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

Offline

Pages: **1**