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# If x + 1 = x^2 and x > 0, then 2x^4 is:

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Math Expert
Joined: 02 Sep 2009
Posts: 64246
If x + 1 = x^2 and x > 0, then 2x^4 is:  [#permalink]

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02 Apr 2020, 09:39
00:00

Difficulty:

55% (hard)

Question Stats:

50% (02:56) correct 50% (02:55) wrong based on 14 sessions

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If $$x + 1 = x^2$$ and $$x > 0$$, then $$2x^4$$ is:

A. $$6 + 4√5$$

B. $$3 + 5√5$$

C. $$7 + 3√5$$

D. $$5 + 3√5$$

E. $$4 + 3√5$$

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Joined: 14 Oct 2019
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Re: If x + 1 = x^2 and x > 0, then 2x^4 is:  [#permalink]

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02 Apr 2020, 10:14
x+1=x^2
or, x = [1± √5]/2
since x>0 , x= [1+√5]/2
or, x^2 = [[1+√5]/2 ]^2
or,X^2 = [3 + √5]/2
or,X^4 = [7 +3√5]/2
or,2×^4 = 7 + 3√5

Option (C)
Re: If x + 1 = x^2 and x > 0, then 2x^4 is:   [#permalink] 02 Apr 2020, 10:14