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Retired Moderator Joined: 07 Jun 2014
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GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
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If xy 0 and x -y, = [#permalink]
Expert's post 00:00

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

_________________

Sandy
If you found this post useful, please let me know by pressing the Kudos Button

Try our free Online GRE Test Manager Joined: 26 Jan 2018
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GRE 1: Q165 V156 Followers: 1

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Re: If xy 0 and x -y, = [#permalink]
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 Joined: 25 Aug 2020
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Re: If xy 0 and x -y, = [#permalink]
Can someone explain this in more detail? I'm not sure what to do on this one  GRE Instructor Joined: 10 Apr 2015
Posts: 3871
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Re: If xy 0 and x -y, = [#permalink]
1
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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) $$\frac{1}{x^9 - y^9}$$

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

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

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

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

_________________

Brent Hanneson – Creator of greenlighttestprep.com
If you enjoy my solutions, you'll like my GRE prep course.  Re: If xy 0 and x -y, =   [#permalink] 03 Oct 2020, 10:23
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