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What is the value of x? (1) (-x)^3 = -x^3 (2) (-x)^2 = -x^2

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What is the value of x? (1) (-x)^3 = -x^3 (2) (-x)^2 = -x^2  [#permalink]

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New post 22 Nov 2018, 02:40
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A
B
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E

Difficulty:

  45% (medium)

Question Stats:

61% (01:18) correct 39% (01:09) wrong based on 136 sessions

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Re: What is the value of x? (1) (-x)^3 = -x^3 (2) (-x)^2 = -x^2  [#permalink]

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New post 22 Nov 2018, 02:47
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Statement 1) \(-x^3 = -x^3\). INSUFFICIENT
Statement 2) \(x^2 = -x^2\)

\(2x^2\) = 0 => x = 0. SUFFICIENT

OPTION: B
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Re: What is the value of x? (1) (-x)^3 = -x^3 (2) (-x)^2 = -x^2  [#permalink]

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New post 22 Nov 2018, 02:47
1
Bunuel wrote:
What is the value of x?

(1) \((-x)^3 = -x^3\)
(2) \((-x)^2 = -x^2\)



Statement 1:

\((-x)^3 = -x^3\)

\(-x^3 = -x^3\)

\(x^3 = x^3\)

x could be 10, o , 100.

NOT sufficient.

Statement 2;

\((-x)^2 = -x^2\)

\(x^2 = -x^2\)

It only possible when x = 0.

Sufficient.

The best answer is B.
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Re: What is the value of x? (1) (-x)^3 = -x^3 (2) (-x)^2 = -x^2  [#permalink]

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New post 22 Nov 2018, 07:30
selim Could you please elaborate your solution?
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Re: What is the value of x? (1) (-x)^3 = -x^3 (2) (-x)^2 = -x^2  [#permalink]

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New post 24 Dec 2018, 01:48
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Re: What is the value of x? (1) (-x)^3 = -x^3 (2) (-x)^2 = -x^2  [#permalink]

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New post 29 Dec 2018, 12:59
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I think the trap in this question lies in tricking you to think that statement 2 will also give a similar solution as statement 1 did. This tends to happen in a lot of DS questions with seemingly similar statements.

Lets dive in!

Statement 1: \((-x)^3 = -x^3\)

An odd power does not change the sign of a number.

So, whether x is positive or negative or 0, \((-x)^3\) will always be equal to \(-x^3\). To illustrate this point, lets take examples:

Case 1: x is 1

\((-1)^3 = -1^3\) which is essentially -1

Case 2: x is 0

\((-0)^3 = -0^3\) which is essentially 0

Case 3: x is -1

\((--1)^3 = --1^3\) which is essentially 1

Since we get no unique value for x, this statement is insufficient

Statement 2: Even power of a number always changes the sign of a number to non-negative.

Thus, \((-x)^2\) will be equal to \(x^2\)
Thus, expression translates to: \(x^2 = -x^2\)
Which implies: \(2x^2 = 0\)
Which implies x=0.

Hence, statement 2 is sufficient and answer is B
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Re: What is the value of x? (1) (-x)^3 = -x^3 (2) (-x)^2 = -x^2   [#permalink] 29 Dec 2018, 12:59
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