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30 Nov 2016, 02:57
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D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
15%
(low)
Question Stats:
75% (00:56) correct
25%
(00:58)
wrong
based on 947
sessions
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Date
Time
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Not Attempted Yet
If x=−|y|, which of the following must be true?
A. y=−x
B. x=y
C. |x|=−y
D. x^2=y^2
E. x^3=y^3
A. y=−x
B. x=y
C. |x|=−y
D. x^2=y^2
E. x^3=y^3
30 Nov 2016, 09:27
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Bunuel
x=−|y|
We can have 2 possibilities -
1. x = -y
2. x = y
Check carefully except Squaring the 2 sides , none must be true ( In all possible cases )...
Answer will be (D)
19 Dec 2016, 11:04
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Bunuel
We are given that x = -|y|, and must determine which answer choice MUST BE TRUE. We can use numerical values for x and y so long they satisfy the equation x = -|y|, and then use them to test each answer choice.
A) y = −x
Answer choice A does not have to be true. For instance, if x = -2 and y = -2, then -2 ≠ 2 and answer choice A is not true.
B) x = y
Answer choice B does not have to be true. For instance, if x = -2 and y = 2, then -2 ≠ 2 and answer choice B is not true.
C) |x| = −y
Answer choice C does not have to be true. For instance, if x = -2 and y = 2, then |-2| ≠ −2 and answer choice C is not true.
D) x^2=y^2
Answer choice D MUST BE TRUE. Using some of the examples for x and y above, we see that in all cases answer choice D must be true.
If x = -2 and y = -2, then (-2)^2 = (-2)^2, and if x = -2 and y = 2, then (-2)^2 = (2)^2.
In fact, no matter what values for x and y we use (which satisfy the equation x = -|y|), x^2 WILL ALWAYS EQUAL y^2.
Since answer choice D must be true, we can stop here.
Answer: D
anyway thanks 
