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If у + |y| = 0, which of the following must be true?

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If у + |y| = 0, which of the following must be true?  [#permalink]

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New post Updated on: 09 Jul 2019, 23:38
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D
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If y + |y| = 0 which of the following must be true?

A. y > 0
B. y ≥ 0
C. y < 0
D. y ≤ 0
E. y = 0

Originally posted by bibha on 07 May 2010, 22:05.
Last edited by Bunuel on 09 Jul 2019, 23:38, edited 2 times in total.
Renamed the topic and edited the question.
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Re: If у + |y| = 0, which of the following must be true?  [#permalink]

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New post 21 Apr 2012, 22:23
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boomtangboy wrote:
If y + | y | = 0, which of the following must be true?
(A) y > 0
(B) y≥0
(C) y < 0
(D) y≤0
(E) y = 0

Why is just E incorrect?


Absolute value properties:
When \(x\leq{0}\) then \(|x|=-x\), or more generally when \(some \ expression\leq{0}\) then \(|some \ expression|={-(some \ expression)}\). For example: \(|-5|=5=-(-5)\);

When \(x\geq{0}\) then \(|x|=x\), or more generally when \(some \ expression\geq{0}\) then \(|some \ expression|={some \ expression}\). For example: \(|5|=5\);

So, \(y+|y|=0\) --> \(|y|=-y\), which means that \(y\leq{0}\).

Answer: D.

As for your doubt: question asks which of the following MUST be true, not COULD be true. Since all negative values of y satisfy \(|y|=-y\) then it's not necessarily true that \(y=0\).

Hope it's clear.
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Re: If у + |y| = 0, which of the following must be true?  [#permalink]

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New post 08 May 2010, 14:55
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Re: If у + |y| = 0, which of the following must be true?  [#permalink]

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New post 18 Feb 2011, 10:30
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banksy wrote:
199. If у + IyI = 0, which of the following must be true?
(A) у > 0
(B) у is no less than 0
(C) у < 0
(D) у is not greater than 0
(E) y = 0


\(y+|y| = 0\) --> \(|y|=-y\). Now, LHS is an absolute value which is never negative hence RHS must also be non-negative: \(-y\geq{0}\) --> \(y\leq{0}\).

Or you can see right away that in order \(y+|y|=0\) to hold true y must be either negative number (for example -3+|-3|=0) or zero (0+|0|=0).

Answer: D.
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Re: If у + |y| = 0, which of the following must be true?  [#permalink]

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New post 15 May 2012, 04:32
I have a question here.. if the the question was y + |y| = 2y , then can we say y>=0? given then 0+0 = 2(0). Please let me know in case I am doing something wrong. Thanks in advance.
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Re: If у + |y| = 0, which of the following must be true?  [#permalink]

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New post 15 May 2012, 04:45
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Re: If у + |y| = 0, which of the following must be true?  [#permalink]

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New post 03 Oct 2012, 03:31
For me the answer is C. (since the question asks MUST be true?)
Can you anyone tell me why C is not correct
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Re: If у + |y| = 0, which of the following must be true?  [#permalink]

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New post 03 Oct 2012, 03:36
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Re: If у + |y| = 0, which of the following must be true?  [#permalink]

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New post 26 Apr 2015, 12:40
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Hi All,

This question is perfect for TESTing VALUES.

We're told that Y + |Y| = 0. We're asked which of the following MUST be true (which means "which of the following is ALWAYS TRUE no matter how many different examples we can come up with?")

The obvious value for Y is 0 (since 0 + |0| = 0)
Eliminate A and C.

Since there are still 3 values remaining, there MUST be other options to consider....

IF....
Y = -1
-1 + |-1| = 0
Eliminate B and E.

There's only one answer left....

Final Answer:

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Re: If у + |y| = 0, which of the following must be true?  [#permalink]

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New post 03 Oct 2017, 17:27
boomtangboy wrote:
If y + | y | = 0, which of the following must be true?

A. y > 0
B. y≥0
C. y < 0
D. y≤0
E. y = 0

Why is just E incorrect?

\(y + |y| = 0\)
\(|y| = 0 - y\)
\(|y| = -y\)

The last expression means that \(y\leq{0}\). That rule can seem odd or counterintuitive.

The variable has a "hidden" negative sign. With the variable, it's hard to remember that there ARE two negative signs on RHS. We just do not (cannot) write the minus sign twice with the variable. These equations are equivalent, where y = -2:

|-2| = -(-2) = 2
|y| = -(y) = -y

So if \(y + |y| = 0\), then \(|y| = -y\) and

\(y\leq{0}\)

Answer D

If none of the above occurs to you or if it makes no sense, pick and list three numbers: negative, 0, and positive.

Use them to try to DISPROVE the answers. Even one example that defies the rule being tested makes "must be true" false.

-2, 0, and 2

A. y > 0
\(y + |y| = 0\). Try y = 0
\(0 + |0| = 0\). That works. \(y\) does not have to be positive. REJECT

B. y≥0. Use -2
\(y + |y| = 0\)
\(-2 + |-2| = 0\). That works. \(y\) can be negative. REJECT

C. y < 0. We know from (A) that \(y\) CAN equal 0. REJECT

D. y≤0. Try 2
\(y + |y| = 0\)
\(2 + |2| \neq{0}\)

We know from (A) that \(y\) can equal 0.
We know from (B) that \(y\) can be negative.

And having tested +2, we know that \(y\) CANNOT be positive.

This expression MUST be true. KEEP

E. y = 0
We know from (B) that \(y\) can be negative. Yes, \(y\) can also be 0. But it does not have to be 0 -- it can be negative, e.g. -2. REJECT

Answer D
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Re: If у + |y| = 0, which of the following must be true?  [#permalink]

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Re: If у + |y| = 0, which of the following must be true?   [#permalink] 13 Mar 2019, 00:24
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