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# If xy 0 and x -y, =

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Retired Moderator
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If xy 0 and x -y, = [#permalink]  19 May 2018, 15:13
Expert's post
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Question Stats:

100% (00:50) correct 0% (00:00) wrong based on 12 sessions
If $$xy \neq 0$$ and $$x \neq -y$$,$$\frac{x^{36}-y^{36}}{(x^{18}+y^{18})(x^{9}+y^{9})}$$ =

(A) $$1$$
(B) $$x^2 - y^2$$
(C) $$x^9 - y^9$$
(D) $$x^{18} - y^{18}$$
(E) $$\frac{1}{x^9 - y^9}$$
[Reveal] Spoiler: OA

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Manager
Joined: 26 Jan 2018
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GRE 1: Q165 V156
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Kudos [?]: 135 [1] , given: 3

Re: If xy 0 and x -y, = [#permalink]  21 May 2018, 21:24
1
KUDOS
(a+b)*(a-b)= a^2-b^2.
Using this formula to further solve the above equation leaves us with option C
Intern
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Re: If xy 0 and x -y, = [#permalink]  27 Sep 2020, 11:33
Can someone explain this in more detail? I'm not sure what to do on this one
GRE Instructor
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Kudos [?]: 4647 [1] , given: 70

Re: If xy 0 and x -y, = [#permalink]  03 Oct 2020, 10:23
1
KUDOS
Expert's post
sandy wrote:
If $$xy \neq 0$$ and $$x \neq -y$$,$$\frac{x^{36}-y^{36}}{(x^{18}+y^{18})(x^{9}+y^{9})}$$ =

(A) $$1$$
(B) $$x^2 - y^2$$
(C) $$x^9 - y^9$$
(D) $$x^{18} - y^{18}$$
(E) $$\frac{1}{x^9 - y^9}$$

$$\frac{x^{36}-y^{36}}{(x^{18}+y^{18})(x^{9}+y^{9})}=\frac{(x^{18}+y^{18})(x^{18}-y^{18})}{(x^{18}+y^{18})(x^{9}+y^{9})}$$

$$=\frac{(x^{18}-y^{18})}{(x^{9}+y^{9})}$$

$$=\frac{(x^{9}+y^{9})(x^{9}-y^{9})}{(x^{9}+y^{9})}$$

$$=x^{9}-y^{9}$$

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Re: If xy 0 and x -y, =   [#permalink] 03 Oct 2020, 10:23
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