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# Quant review #64

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Director
Joined: 25 Oct 2008
Posts: 580
Location: Kolkata,India

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28 Jul 2009, 07:34
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Hey guys,what is the value of cube root(-64)?Is'nt any -ive sign under a root undefined?
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http://gmatclub.com/forum/countdown-beginshas-ended-85483-40.html#p649902

Manager
Joined: 30 May 2009
Posts: 213

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28 Jul 2009, 07:47
Tejal, I think you are getting confused between square root and cube root. Cube root can definitely have -ve numbers. cuberoot(-64) = -4

But squareroot(-64) is imaginary and not defined
Senior Manager
Joined: 18 Jun 2009
Posts: 351
Location: San Francisco

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28 Jul 2009, 09:09
Tejal

Think in this way, reverse engineer

square of any number +ve or -ve can never be -ve therefore square root of a negative number is imaginary

but cube root of a +ve number is +ve and -ve number is -ve therefore cuberoot of a negative number is possible and is the cuberoot of the number with a -ve sign.
Manager
Joined: 03 Jul 2009
Posts: 103
Location: Brazil

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28 Jul 2009, 11:46
Just use numbers and you will see it is quite simple:

(-4)*(-4)*(-4)
(16)*(-4)
-64
Re: Quant review #64   [#permalink] 28 Jul 2009, 11:46
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