If x^2 – 4x = 5, then one possible value of x – 4 = - The Beat The GMAT Forum

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

by Brent@GMATPrepNow » Wed Aug 05, 2020 6:17 am

BTGModeratorVI wrote: ↑
Sun Aug 02, 2020 6:59 am
If x^2 – 4x = 5, then one possible value of x – 4 =

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

Answer: B
Source: Manhattan prep

x^2 – 4x = 5
Rearrange to get: x^2 – 4x - 5 = 0
Factor: (x - 5)(x + 1) = 0
So, either x = 5 or x = -1

If x = 5, then x - 4 = 5 - 4 = 1 [not among the answer choices]
If x = -1, then x - 4 = (-1) - 4 = -5. Great!

Answer: B

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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

by Scott@TargetTestPrep » Mon Aug 10, 2020 3:19 am

BTGModeratorVI wrote: ↑
Sun Aug 02, 2020 6:59 am
If x^2 – 4x = 5, then one possible value of x – 4 =

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

Answer: B

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.

Answer: B

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