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# If x^2 + 2x – 8 = 0, then x is either –4 or

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Math Expert
Joined: 02 Sep 2009
Posts: 48096
If x^2 + 2x – 8 = 0, then x is either –4 or  [#permalink]

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29 Oct 2017, 01:32
1
00:00

Difficulty:

5% (low)

Question Stats:

90% (00:23) correct 10% (00:10) wrong based on 82 sessions

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If x^2 + 2x – 8 = 0, then x is either –4 or

(A) –2
(B) –1
(C) 0
(D) 2
(E) 8

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Re: If x^2 + 2x – 8 = 0, then x is either –4 or  [#permalink]

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29 Oct 2017, 08:09
1
Bunuel wrote:
If x^2 + 2x – 8 = 0, then x is either –4 or

(A) –2
(B) –1
(C) 0
(D) 2
(E) 8

$$x^2 + 2x – 8 = 0$$

Or, $$x^2 + 4x - 2x - 8 = 0$$

Or, $$x(x + 4 ) -2 (x + 4) = 0$$

Or, x = 2 and x = -4

Thus, answer will be (D) 2
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Intern
Joined: 04 May 2015
Posts: 17
Re: If x^2 + 2x – 8 = 0, then x is either –4 or  [#permalink]

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01 Nov 2017, 08:44
1
x^2+2x–8 =0
: x^2+4x−2x−8=0
: x(x+4)−2(x+4)=0
: (x-2)(x+4)=0
x=2, x= -4
ans. D.
Intern
Joined: 25 May 2017
Posts: 10
GMAT 1: 750 Q49 V44
Re: If x^2 + 2x – 8 = 0, then x is either –4 or  [#permalink]

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04 Nov 2017, 18:32
So, we're starting off with

$$x^2$$+ 2x – 8 = 0

There is no need to dive into a series of long steps. We just need to focus on the 2 numbers highlighted below:

$$x^2$$ + 2x – 8 = 0

Two numbers ADDED should give you 2, and MULTIPLIED should give you -8
4 and -2 work.

To get the final solution you alway 'flip' the signs. So the two solutions are -4 and 2.

Answer is D
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Re: If x^2 + 2x – 8 = 0, then x is either –4 or &nbs [#permalink] 04 Nov 2017, 18:32
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