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# If x^2 – 4x = 5, then one possible value of x – 4 =

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Re: If x^2 – 4x = 5, then one possible value of x – 4 = [#permalink]
x^2 - 4x -5 = 0
x^2 - 5x + 1x - 5 = 0
x(x-5) + 1(x-5) = 0
(x-5)(x+1)=0
x = 5
or x = -1

Therefore,
x-4 = 5-4 = 1
or x-4 = -1-4 = -5
Since only -5 is in the options, it is the correct answer
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Re: If x^2 – 4x = 5, then one possible value of x – 4 = [#permalink]
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Bunuel wrote:
If x^2 – 4x = 5, then one possible value of x – 4 =

A. -9
B. -5
C. -3
D. -1
E. 5

Solution:

We will set the equation equal to 0, factor the quadratic, and find the zeros:

x^2 - 4x - 5 =0

(x - 5)(x + 1) = 0

x = 5 OR x = -1

We see that x - 4 could equal 1 or -5.

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Re: If x^2 – 4x = 5, then one possible value of x – 4 = [#permalink]
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Hi all,

For ALL second grade equation questions in GMAT, you should know this trick well explained by the MIT technology review: technologyreview.es/s/11687/un-matematico-revoluciona-la-resolucion-de-ecuaciones-de-segundo-grado

x^2+Bx+C,being R and S the solutions

-B = R+S
C = R*S

Then, you will be able to solve questions very quickly (such as this one)
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Re: If x^2 4x = 5, then one possible value of x 4 = [#permalink]
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Re: If x^2 4x = 5, then one possible value of x 4 = [#permalink]
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