(2 + 7^1/2) (4 − 7^1/2) (−2x) =

Question

(2 + \sqrt{7}) (4 − \sqrt{7}) (−2x) =

(A)  78x − 4x \sqrt{7}

(B)  \sqrt{7}x

(C)  −2x − 4x \sqrt{7}

(D)  –2x

(E)  4x \sqrt{7}

KarishmaB · Answer

(2 + \sqrt{7}) (4 − \sqrt{7}) (−2x) = (1 + 2\sqrt{7})(-2x)

= -2x -4x\sqrt{7}

Kinshook · Answer

(2 + \sqrt{7}) (4 − \sqrt{7}) (−2x) = 
 =(8 +4 \sqrt{7} -2\sqrt{7}-7)(-2x) 
 =(1+2\sqrt{7})(-2x) 
 =-2x-4x\sqrt{7}

IMO C

bebs · Answer

Kinshook  There is a typo in your solution. The answer is C, which is what you got, not D.

Kinshook · Answer

OK. Thanks for noticing.
Corrected

ScottTargetTestPrep · Answer

Simplifying, we have:

(8 - 2√7 + 4√7 - 7)(-2x)

(1 + 2√7)(-2x)

-2x -4x√7

Answer: C

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