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

Question

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

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

Bunuel · Answer

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.

AKG1593 · Answer

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.

WoundedTiger · Answer

(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

BrushMyQuant · Answer

We need to find the value of  (1+\sqrt{5})(1-\sqrt{5})

Given expression is of the form (a+b)*(a-b) where 
 
  1 = a  
   \sqrt{5}  = b   
And 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!

Watch the following video to MASTER Roots

https://www.youtube.com/watch?v=5oAec-Y6kOQ

totaltestprepNick · Answer

A https://www.youtube.com/watch?v=qB1d6LNVEO0 Nick Slavkovich, GMAT/GRE tutor with 20+ years of experience tutoring@totaltestprep.net

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