Math Is Fun Forum

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

You are not logged in.

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

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

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

Offline

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

Bob
Administrator
Registered: 2010-06-20
Posts: 10,058

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


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
Sometimes I deliberately make mistakes, just to test you!  …………….Bob smile

Offline

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

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

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

Offline

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

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

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

Offline

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

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

Re: Little question about exponents

And why would it be that way ?

Offline

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

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

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

Offline

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

Bob
Administrator
Registered: 2010-06-20
Posts: 10,058

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


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
Sometimes I deliberately make mistakes, just to test you!  …………….Bob smile

Offline

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

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

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 ?

Offline

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

Bob
Administrator
Registered: 2010-06-20
Posts: 10,058

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


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
Sometimes I deliberately make mistakes, just to test you!  …………….Bob smile

Offline

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

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

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 )

Offline

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

Bob
Administrator
Registered: 2010-06-20
Posts: 10,058

Re: Little question about exponents

Yes, that looks ok to me.

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

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
Sometimes I deliberately make mistakes, just to test you!  …………….Bob smile

Offline

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

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

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

Offline

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

Bob
Administrator
Registered: 2010-06-20
Posts: 10,058

Re: Little question about exponents

Evaluate

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
Sometimes I deliberately make mistakes, just to test you!  …………….Bob smile

Offline

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

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

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)

Offline

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

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

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

Offline

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

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

Re: Little question about exponents

Thanks bobbym

Offline

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

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,049

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

Offline

#18 2013-07-02 10:57:08

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

Re: Little question about exponents

Ah ok, thank you!

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

Offline

Board footer

Powered by FluxBB