Rational numbers Question (Source GMAT prep)

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mach81: Newbie | Next Rank: 10 Posts; Posts: 2; Joined: Mon Sep 10, 2007 5:18 am

by mach81 » Wed Sep 12, 2007 5:09 pm

What is the value of

sqrt(9+sqrt80) + sqrt(9-sqrt80)

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Source: Beat The GMAT — Problem Solving | Wed Sep 12, 2007 5:09 pm

keepsmilinyaar: Senior | Next Rank: 100 Posts; Posts: 43; Joined: Sun Feb 18, 2007 5:59 am

by keepsmilinyaar » Wed Sep 12, 2007 8:25 pm

what are the options?

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wizardofwashington: Senior | Next Rank: 100 Posts; Posts: 71; Joined: Wed Aug 22, 2007 12:29 pmFollowed by: 1 member; Location: USA; Thanked: 12 times

Your question is probably incomplete??

by wizardofwashington » Wed Sep 12, 2007 8:41 pm

Looks like this in an incomplete question. I dug around the web (thanks to Google) and found something very similar on Test Magic. Mach, may be you can verify if this is indeed correct or not. The question should be:
(sqrt(9+sqrt80)+sqrt(9-sqrt80) )^2

Solution, which I know most of you will do with your eyes closed, is here:

Use the formula (a+b)^2 = a^2 + b^2 + 2ab

9+sqrt80+9-sqrt80 + 2*sqrt(9^2 - 80)
= 18 + 2*1 =20 (thanks to Mits83 from TestMagic)

For those who care, here is the link to the TestMagic thread:
https://www.urch.com/forums/gmat-problem ... p-2-a.html

A falling tree resounds... but a forest grows in silence...

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