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# Can some one please explain this to me

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Senior Manager
Joined: 07 Feb 2008
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15 Jun 2008, 12:45
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Can someone please explain to me how you arrive at the answer
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square root problem.doc [48.5 KiB]

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Director
Joined: 14 Oct 2007
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Location: Oxford
Schools: Oxford'10

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15 Jun 2008, 13:29
Vavali wrote:
Can someone please explain to me how you arrive at the answer

$$(\sqrt{9 + \sqrt{80}} + \sqrt{9-\sqrt{81}})^2$$

expanding out you get

$$(9-\sqrt{80}) + (9+\sqrt{80}) + 2\sqrt{9+\sqrt{80}}\sqrt{9-\sqrt{80}}$$
simplify:
$$18 + 2\sqrt{(9+\sqrt{80})(9-\sqrt{80})} = 18 + 2 =20$$

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Re: Can some one please explain this to me   [#permalink] 15 Jun 2008, 13:29
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