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confusion in solving this gmat prob

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by quantskillsgmat » Mon Jan 09, 2012 10:47 pm
can anyone explain me why square root of x is always taken as positive in GMAT
eg
Q SQUARE ROOT OF 4+CUBE ROOT OF 4+FORUTH ROOT OF 4 is
a)between 1 and 2
b)between 2 and 3
c)between 3 and 4
d)more than 4
here if i take positive roots then ans is more than 4 but if i consider both positive and negative various ans are possible.
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Source: — Problem Solving |

by neelgandham » Mon Jan 09, 2012 11:01 pm
As far as I know

The term 'Square root' in GMAT is used to refer to the principal square root(The positive square root). Check the properties section here -> https://en.wikipedia.org/wiki/Square_root for more information regarding principal square root.

Why is it referred to the principal square root ? I really don't know. We shall wait for the experts to answer.
Anil Gandham
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by Anurag@Gurome » Mon Jan 09, 2012 11:09 pm
quantskillsgmat wrote:can anyone explain me why square root of x is always taken as positive in GMAT...
There is a difference between square root of x and √x. Any number x have two square roots, a negative one and a positive one, i.e. √x and -√x. But √x always represents only the positive root.

For example, 4 have two square roots 2 and - 2. But √4 = 2 not -2.

If the question says square root of 4, then your logic is correct. But I believe the question says √4. Hence, only the positive root has to be considered.

Similarly, any number x has four fourth roots, one positive, one negative, and two imaginary roots. But if the symbol of fourth root is used, then we have to take the positive roots only.
Anurag Mairal, Ph.D., MBA
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by archit.job » Sat Jan 14, 2012 1:28 am
Dear Anurag Sir,

I would like to confirm one thing..that if √4 = +2 & squareroot 4 =±2 agreed,

but we cannot say that √-4 =-2 it has to be a complex output.
So how can √4 be = only +4
Kindly explain.
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