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# If x + y = -3 and x2 + y2 = 12, what is the value of 2xy?

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If x + y = -3 and x2 + y2 = 12, what is the value of 2xy? [#permalink]  19 May 2018, 16:15
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100% (01:07) correct 0% (00:00) wrong based on 3 sessions
If $$x + y = -3$$ and $$x^2 + y^2 = 12$$, what is the value of 2xy?

[Reveal] Spoiler: OA
-3

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Re: If x + y = -3 and x2 + y2 = 12, what is the value of 2xy? [#permalink]  19 May 2018, 22:28
Given,$$x + y = -3$$ and $$x^2 + y^2 = 12$$

Let us square $$(x+y)$$:

$$x^2 + y^2 + 2xy = 9$$
or, $$12 + 2xy = 9$$; from the question stem we have $$x^2 + y^2 = 12$$
or, $$2xy = -3$$
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Re: If x + y = -3 and x2 + y2 = 12, what is the value of 2xy?   [#permalink] 19 May 2018, 22:28
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