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# If x^2 – 2xy = 84 and x – y = –10, what is the value of |y|?

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Math Expert
Joined: 02 Sep 2009
Posts: 58320
If x^2 – 2xy = 84 and x – y = –10, what is the value of |y|?  [#permalink]

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28 Jan 2019, 04:00
00:00

Difficulty:

25% (medium)

Question Stats:

74% (02:06) correct 26% (02:43) wrong based on 106 sessions

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If $$x^2 - 2xy = 84$$ and $$x - y = -10$$, what is the value of |y|?

A. 0
B. 2
C. 3
D. 4
E. 6

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Joined: 31 Oct 2013
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Concentration: Accounting, Finance
GPA: 3.68
WE: Analyst (Accounting)
Re: If x^2 – 2xy = 84 and x – y = –10, what is the value of |y|?  [#permalink]

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28 Jan 2019, 04:06
5
Bunuel wrote:
If $$x^2 - 2xy = 84$$ and $$x - y = -10$$, what is the value of |y|?

A. 0
B. 2
C. 3
D. 4
E. 6

$$(x - y)^2 = (-10)^2$$

$$x^2 - 2xy + y^2 = 100$$

$$84 + y^2 = 100$$

$$y^2 = 16$$

y = + 4 or -4.

|y| = |4| = 4.

Re: If x^2 – 2xy = 84 and x – y = –10, what is the value of |y|?   [#permalink] 28 Jan 2019, 04:06
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