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ANOVA - Question

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by ajith » Fri Mar 05, 2010 12:43 am
Any thoughts on this question - I know its quite basic but I don't agree with the books explanation for some reason

[Sorry Jas, I was trying to move the question to PS forum and goofed up, reposting the question]
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by harsh.champ » Fri Mar 05, 2010 12:58 am
ajith wrote:Any thoughts on this question - I know its quite basic but I don't agree with the books explanation for some reason

[Sorry Jas, I was trying to move the question to PS forum and goofed up, reposting the question]
Main pt. to remember - Root x = |x|
Hence sqrt(4) = 2.
So we get -2^(4) = -16

Ans. must be -16 + 2 = -14
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by harsh.champ » Fri Mar 05, 2010 12:59 am
1)x^2 =4 => x = +2 or x=-2

2)sqrt(4) = 2(always)

This is a very common trap in maths.
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by JasLamba » Fri Mar 05, 2010 1:03 am
Thanks for the reply.

I don't understand how we get to -16 and not +16. -2^4 is supposed to be positive right?

16+2 = 18?
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by ajith » Fri Mar 05, 2010 1:20 am
JasLamba wrote:Thanks for the reply.

I don't understand how we get to -16 and not +16. -2^4 is supposed to be positive right?

16+2 = 18?

Jas,

it is just -1* 2^4, it is always -16 and not 16

2^(-4 ) on the other hand is 1/2^4 = 1/16
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by harsh.champ » Fri Mar 05, 2010 1:22 am
JasLamba wrote:Thanks for the reply.

I don't understand how we get to -16 and not +16. -2^4 is supposed to be positive right?

16+2 = 18?
It should be then written as (-2)^(2sqrtx).

I think over here,it means - (2)^(2sqrtx).

It would be kind if any tutor would like to throw some light regarding notations in the Quant section.

Thanks!!!
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by JasLamba » Fri Mar 05, 2010 1:35 am
I was under the impression that -2^4 is -2*-2*-2*-2 which means its positive?

Isn't a negative number to an even exponent positive?


The explanation of the book agrees with your initial thought hash.champ.

Glad I am making these mistakes now ...
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by harsh.champ » Fri Mar 05, 2010 1:42 am
JasLamba wrote:I was under the impression that -2^4 is -2*-2*-2*-2 which means its positive?

Isn't a negative number to an even exponent positive?


The explanation of the book agrees with your initial thought hash.champ.

Glad I am making these mistakes now ...
I want to know:-Is this question from GMATPrep ??
I doubt that GMAT will trick us in notations..
Basically they are not testing us how we perceive the symbols (-2)^4 or - (2)^4 .
Also if some GMAT prep company instructor can throw some light in this regard ,it will be helpful.Can we highlight this thread on the main forum ( I guess mods can do that) as it is very imp. to know whether the explanation in the book is correct or not??
Getting this ques. wrong will be like throwing away easy marks in the drain.

Any feedback will be appreciated.
It takes time and effort to explain, so if my comment helped you please press Thanks button :)



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by ajith » Fri Mar 05, 2010 2:49 am
harsh.champ wrote: I want to know:-Is this question from GMATPrep ??
I doubt that GMAT will trick us in notations..
Basically they are not testing us how we perceive the symbols (-2)^4 or - (2)^4 .
Also if some GMAT prep company instructor can throw some light in this regard ,it will be helpful.Can we highlight this thread on the main forum ( I guess mods can do that) as it is very imp. to know whether the explanation in the book is correct or not??
Getting this ques. wrong will be like throwing away easy marks in the drain.

Any feedback will be appreciated.
-2^4 is -1*2^4

(-2)^4 is -2*-2*-2*-2

"The standard order of operations, or precedence, is expressed in the following chart.

exponents and roots
multiplication and division
addition and subtraction"

[https://en.wikipedia.org/wiki/Order_of_operations]

considering -2^4's case we need to do exponent operation first and then the multiplication operation.
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by JasLamba » Fri Mar 05, 2010 3:22 am
this question is from ANOVA Math Guide. NOT a real GMAT prep Question.

I guess the take away is

-2^4 = -16 because we do the 2^4 = 16 and multiply it by -1.

(-2)^4 = 16 because we are multiplying -2*-2*-2*-2

So notation is the key here to properly understand what we are talking about. Thanks for the help guys.
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by dtwea » Sun Mar 07, 2010 6:00 am
JasLamba wrote:this question is from ANOVA Math Guide. NOT a real GMAT prep Question.

I guess the take away is

-2^4 = -16 because we do the 2^4 = 16 and multiply it by -1.

(-2)^4 = 16 because we are multiplying -2*-2*-2*-2

So notation is the key here to properly understand what we are talking about. Thanks for the help guys.
Or if one didn't know all this principle

-2^4 = -1 x 2^4 two separate numbers. Like this u don't even have to think about which to multiply first or second. You have two separate numbers, one negative and another positive and know your answer must be negative.
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