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# If a = (x + y)2 and b = x2 + y2 and xy > 0, which of the fol

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If a = (x + y)2 and b = x2 + y2 and xy > 0, which of the fol [#permalink]  20 May 2018, 10:51
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77% (00:10) correct 22% (00:04) wrong based on 9 sessions
If $$a = (x + y)^2$$ and $$b = x^2 + y^2$$ and $$xy > 0$$, which of the following must be true?
Indicate all such statements.

A. a = b
B. a > b
C. a is positive
[Reveal] Spoiler: OA

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Re: If a = (x + y)2 and b = x2 + y2 and xy > 0, which of the fol [#permalink]  20 Jun 2018, 01:12
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expanding a we get, a = $$x^2 + y^2 + 2xy$$
b = $$x^2 + y^2$$
Since $$xy$$ > 0; $$2xy$$ > $$0$$
therefore a is greater than b by $$2xy$$; Hence option a is not correct but option b is correct

we know square of any number is always +ve hence$$x^2 + Y^2$$ is +ve and when it is added to $$2xy$$ the result is +ve
option c is also correct.

Hence only option b and c are correct.
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Re: If a = (x + y)2 and b = x2 + y2 and xy > 0, which of the fol   [#permalink] 20 Jun 2018, 01:12
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