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Please help!!!

by Nidhs » Sun Mar 09, 2008 5:26 pm
I couldn't think of a better way to write this. I f someone understands what ive written...can someone please explain it to me. The problem is from GMATPrep and i have my exam tom.

(rt((9+rt80) + (9-rt80))rt )^2
OA is 20
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Re: Please help!!!

by camitava » Sun Mar 09, 2008 9:18 pm
Nidhs wrote:I couldn't think of a better way to write this. I f someone understands what ive written...can someone please explain it to me. The problem is from GMATPrep and i have my exam tom.

(rt((9+rt80) + (9-rt80))rt )^2
OA is 20
Can you please give a snap-shot so that it will be easier to understand. I am not getting anything!
Correct me If I am wrong


Regards,

Amitava
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by blue_lotus » Mon Mar 10, 2008 2:21 am
[Sqrt(9 + sqrt(80)) + sqrt (9 -sqrt(80) ] ^2

= (a + b) ^2 => a^2 + b^2 + 2*a*b

=> [Sqrt(9 + sqrt(80))]^2 + [sqrt (9 -sqrt(80) ] ^2 + 2 [Sqrt(9 + sqrt(80))] [sqrt (9 -sqrt(80) ]
=>9 + sqrt(80) + 9 - sqrt(80) + 2 [Sqrt(9 + sqrt(80))] [sqrt (9 -sqrt(80) ]
=>18 + 2 [Sqrt(9 + sqrt(80))] [sqrt (9 -sqrt(80) ]
=>18 + 2 [ sqrt ( (9 + sqrt(80) *(9 -sqrt(80) ) ] -----by taking sqrt common as a^m * b^m = (ab)^m , here m = 1/2
Notice that the data inside square bracket is of form (a+b) (a-b) = a^2 - b^2
=> 18 + 2[ sqrt ( 81 - 80) ]
=>18 +2 (1)
=>20
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