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

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Intern
Joined: 07 Nov 2012
Posts: 12
What is the value of x^2 - 4y^2?  [#permalink]

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Updated on: 08 Nov 2012, 03:13
2
00:00

Difficulty:

15% (low)

Question Stats:

79% (00:33) correct 21% (00:44) wrong based on 112 sessions

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

(1) x - 2y = 0
(2) x + 2y = 0

Originally posted by derekgmat on 08 Nov 2012, 03:10.
Last edited by Bunuel on 08 Nov 2012, 03:13, edited 1 time in total.
Edited the question.
Math Expert
Joined: 02 Sep 2009
Posts: 49251
Re: What is the value of x^2 - 4y^2?  [#permalink]

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08 Nov 2012, 03:16
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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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Re: What is the value of x^2 - 4y^2?  [#permalink]

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08 Nov 2012, 03:25
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]

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26 Sep 2017, 17:36
$$x^2-4y^2$$ = $$x^2-(2y)^2$$ = $$(x+2y)(x-2y)$$

So the question becomes $$(x+2y)(x-2y)$$ = ?

Either statement gives us the answer as 0. Hence the answer is D
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Re: What is the value of x^2 - 4y^2? &nbs [#permalink] 26 Sep 2017, 17:36
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