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# What is the value of x^2 - 4y^2?

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What is the value of x^2 - 4y^2? [#permalink]  08 Nov 2012, 02:10
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Difficulty:

15% (low)

Question Stats:

78% (01:28) correct 22% (00:30) wrong based on 58 sessions
What is the value of x^2 - 4y^2?

(1) x - 2y = 0
(2) x + 2y = 0
[Reveal] Spoiler: OA

Last edited by Bunuel on 08 Nov 2012, 02:13, edited 1 time in total.
Edited the question.
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Re: What is the value of x^2 - 4y^2? [#permalink]  08 Nov 2012, 02:16
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What is the value of x^2 - 4y^2?

Remember that $$a^2-b^2=(a-b)(a+b)$$. Thus $$x^2 - 4y^2=x^2-(2y)^2=(x-2y)(x+2y)$$.

(1) x - 2y = 0. Since one of the multiple is zero, then the product is zero. Sufficient.
(2) x + 2y = 0. The same here: since one of the multiple is zero, then the product is zero. Sufficient.

Hope it's clear.
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Intern
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Re: What is the value of x^2 - 4y^2? [#permalink]  08 Nov 2012, 02:25
Thanks alot!

That is actually quite easy, but had me stumped for a long time.... More practice required....
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Re: What is the value of x^2 - 4y^2? [#permalink]  10 Feb 2014, 04:59
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Re: What is the value of x^2 - 4y^2?   [#permalink] 10 Feb 2014, 04:59
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