Square root concept in GMAT

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sunnyjohn: Master | Next Rank: 500 Posts; Posts: 344; Joined: Mon Sep 14, 2009 5:40 amFollowed by: 3 members; Thanked: 28 times; GMAT Score:700

by sunnyjohn » Sat Jul 30, 2011 8:11 am

Hi,

I was reading Master the GMAT maths concepts about square root. According to it, GMAT only consider positive value of square root. For example-

4th root of 16 = -2 or 2

GMAT only consider 2. Isn't it wierd ?

Can any expert please comment on this?

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Source: Beat The GMAT — Problem Solving | Sat Jul 30, 2011 8:11 am

Frankenstein: Legendary Member; Posts: 1448; Joined: Tue May 17, 2011 9:55 amFollowed by: 53 members; Location: India; Thanked: 375 times

by Frankenstein » Sat Jul 30, 2011 8:28 am

Hi,
It is not just on GMAT. Square root of number is always the positive one. Never consider the negative root.
sqrt(4) = +2 only, not 2 or -2.
Some of the school books might have given both roots. But, it is incorrect.
But, if you are given x^2 = 4, find x. The answer would be x =+2 or -2.

Cheers!

Things are not what they appear to be... nor are they otherwise

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BlindVision: Master | Next Rank: 500 Posts; Posts: 253; Joined: Fri Dec 26, 2008 8:39 pmFollowed by: 1 member; Thanked: 8 times

by BlindVision » Sat Jul 30, 2011 3:32 pm

If I may add the obvious, no number when multiplied an even number of times will yield a negative number.

However, for odd roots (cube, 5th, 7th, etc.) the root will have the same sign as the base:

3 sqrt(-27) = -3 not +/- 3

Life is a Test

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tpr-becky: GMAT Instructor; Posts: 509; Joined: Wed Apr 21, 2010 1:08 pmFollowed by: 85 members; Location: Irvine, CA; Thanked: 199 times; GMAT Score:750

by tpr-becky » Sat Jul 30, 2011 8:04 pm

If the GMAT puts the number under the square root then they only consider the positive root.

Thus sqrt25 = 5

However if the gmat says the square of a number is -- then you need to consider positive and negative.

Thus x^2 = 25 means that x = 5 or -5

Becky
Master GMAT Instructor
The Princeton Review
Irvine, CA

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sunnyjohn: Master | Next Rank: 500 Posts; Posts: 344; Joined: Mon Sep 14, 2009 5:40 amFollowed by: 3 members; Thanked: 28 times; GMAT Score:700

by sunnyjohn » Sun Jul 31, 2011 8:44 pm

Thanks everyone..

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