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: 324

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: 7,846

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

Children are not defined by school ...........The Fonz

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: 324

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****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 108,752

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.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 324

And why would it be that way ?

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 108,752

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.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,846

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

Children are not defined by school ...........The Fonz

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: 324

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: 7,846

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

Children are not defined by school ...........The Fonz

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: 324

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: 7,846

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

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 324

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: 7,846

Evaluate

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: 324

{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****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 108,752

You can use codecogs to latex that expression correctly.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 324

Thanks bobbym

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,030

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

The knowledge of some things as a function of age is a delta function.

Offline

**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 324

Ah ok, thank you!

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

Offline

Pages: **1**