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What is the range of the roots of ||x – 1| – 2| = 1?

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What is the range of the roots of ||x – 1| – 2| = 1?  [#permalink]

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New post 29 Aug 2017, 02:02
3
14
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A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

61% (01:48) correct 39% (01:47) wrong based on 511 sessions

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Re: What is the range of the roots of ||x – 1| – 2| = 1?  [#permalink]

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New post 30 Aug 2017, 03:52
8
Bunuel wrote:
What is the range of the roots of \(||x – 1| – 2| = 1\)?

A. 0
B. 2
C. 4
D. 6
E. 8


Another approach

Let \(z = x -1\)

\(||z| – 2| = 1\).............square both sides

\(z^2-4|z|+4=1\)

\(z^2-4|z|+3=0\)

\((|z|-3)(|z|-1)=0\)

\(|z|=3\) or \(|z|=1\)

substitute z from above

\(x–1=3\) or \(x–1=-3\)
\(x=4\) or \(x=-2\)

OR

\(x–1=1\) or \(x–1=-1\)
\(x=2\) or \(x=0\)

Range = Max value - min value

\(R=4-(-2)=4+2=6\)

Answer: D
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Re: What is the range of the roots of ||x – 1| – 2| = 1?  [#permalink]

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New post 29 Aug 2017, 02:44
4
2
Bunuel wrote:

Fresh GMAT Club Tests' Challenge Question:



What is the range of the roots of \(||x – 1| – 2| = 1\)?

A. 0
B. 2
C. 4
D. 6
E. 8


||x – 1| – 2| = 1
|x – 1| – 2 = 1 or |x – 1| – 2 = -1

if |x – 1| – 2 = 1
|x – 1| = 3
x – 1 = 3 or x – 1 = -3
giving us x = 4, -2

if |x – 1| – 2 = -1
|x – 1| = 1
x – 1 = 1 or x – 1 = -1
giving us x = 2, 0

now we have x=-2,0,2,4
range will be 4+2 = 6
D
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What is the range of the roots of ||x – 1| – 2| = 1?  [#permalink]

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New post 31 Aug 2017, 20:22
1
1
The expression is in the form ||a| - 2| = 1

There are 4 possibilities, when trying to solve this equation
|-a -2| = 1
There are 2 options:
-(-a -2) = 1 => a +2 = 1 => a = -1
(-a - 2) = 1 => -a = 3 => a = -3

|a - 2| = 1
There are 2 options:
-(a - 2) = 1 => -a + 2 = 1 => a = 1
(a - 2) = 1 => a = 3

Hence, there are 4 values for a which are -3,-1,1,3

Coming back to the question, if we substitute a to be x-1

x - 1 = -3 => x = -2
x - 1 = -1 => x = 0
x - 1 = 1 => x = 2
x - 1 = 3 => x = 4

Hence, the range of the values is 6(Option D)
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Re: What is the range of the roots of ||x – 1| – 2| = 1?  [#permalink]

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New post 31 Aug 2017, 22:20
1
the values are
X-3=1
-X+3 = 1
-X-1 = 1
X+1 = 1

the values X are { 4, 2, 0, -2}

hence range = 4-(-2)
6
Answer D
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Re: What is the range of the roots of ||x – 1| – 2| = 1?  [#permalink]

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New post 02 Sep 2017, 00:34
2
||x-1|-2|=1

Removing the outer modulus, we get
|x-1|-2 = 1 (or) -1

|x-1|= 3 (or) 1

Now, if we remove the modulus for |x-1| we will get the following four possible values for x

x-1= 3 (or) -3 => x= 4 (or) -2
X-1= 1 (or) -1 => x= 2 (or) 0

Hence the four possible values of x are (-2,0,2,4)
=> Range= 4- (-2) = 6

Ans-> Option D
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What is the range of the roots of ||x – 1| – 2| = 1?  [#permalink]

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New post 17 Sep 2018, 03:54
1
I just applied a rule for complex absolute value equations:

If the equation contains 1 variable and 1 or more than 1 constant(s) in 1 or more than 1 absolute value expressions, the only two cases we have to consider are (1) that the expressions have the same sign and (2) that they have different signs.

Applied to the question here I computed the following:

case (1):

(x-1)-2=1
x-3=1
x=4

case (2)
-(x-1)-2=1
-x+1-2=1
-x-1=1
-2=x

Since we are asked for the range (= highest value-lowest value), we have to perform this final step to get to the answer: 4-(-2)=6.

Please hit Kudos if you liked this approach :)
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Re: What is the range of the roots of ||x – 1| – 2| = 1?  [#permalink]

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New post 24 Dec 2018, 04:53
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Re: What is the range of the roots of ||x – 1| – 2| = 1?   [#permalink] 24 Dec 2018, 04:53
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