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(1+5^1/2)(1-5^1/2)=

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Bunuel
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(1+5^1/2)(1-5^1/2)= [#permalink] (1+5^1/2)(1-5^1/2)=   02 Jan 2014, 06:40
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93% (00:23) correct 7% (00:50) wrong based on 1492 sessions
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\((1+\sqrt{5})(1-\sqrt{5})=\)

(A) -4
(B) 2
(C) 6
(D) \(-4-2\sqrt{5}\)
(E) \(6-2\sqrt{5}\)
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A
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Bunuel
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Re: (1+5^1/2)(1-5^1/2)= [#permalink] (1+5^1/2)(1-5^1/2)=   02 Jan 2014, 06:42
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SOLUTION

\((1+\sqrt{5})(1-\sqrt{5})=\)

(A) -4
(B) 2
(C) 6
(D) \(-4-2\sqrt{5}\)
(E) \(6-2\sqrt{5}\)

Apply \((a+b)(a-b)=a^2-b^2\): \((1+\sqrt{5})(1-\sqrt{5})=1-5=-4\).

Answer: A.
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Re: (1+5^1/2)(1-5^1/2)= [#permalink] (1+5^1/2)(1-5^1/2)=   02 Jan 2014, 06:54
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Quite a simple question:(a+b)*(a-b)=a^2-b^2
So,(1+5^1/2)(1-5^1/2)=1-5=-4
Option A should be the answer.
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Re: (1+5^1/2)(1-5^1/2)= [#permalink] (1+5^1/2)(1-5^1/2)=   03 Jan 2014, 00:41
(1+\sqrt{5})(1-\sqrt{5})=

(A) -4
(B) 2
(C) 6
(D) -4-2\sqrt{5}
(E) 6-2\sqrt{5}

Sol: We know a^2-b^2= (a-b)(a+b).

Therefore the above can be re-written as (1^2-\sqrt{5}^2)------>(1-5)= -4 Ans A
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Re: (1+5^1/2)(1-5^1/2)= [#permalink] (1+5^1/2)(1-5^1/2)=   02 Oct 2022, 04:29
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We need to find the value of \((1+\sqrt{5})(1-\sqrt{5})\)

Given expression is of the form (a+b)*(a+b) and we know that

(a+b)*(a+b) = \(a^2 - b^2\)

=> \((1+\sqrt{5})(1-\sqrt{5})\) = \(1^2 - \sqrt{5}^2\) = 1 - 5 = -4

So, Answer will be A
Hope it helps!
gmatclubot
Re: (1+5^1/2)(1-5^1/2)= [#permalink]
02 Oct 2022, 04:29
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Bunuel
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