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# If y^(-2) + 2y^(-1) -15 = 0, which of the following could be the value

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Math Expert
Joined: 02 Sep 2009
Posts: 47157
If y^(-2) + 2y^(-1) -15 = 0, which of the following could be the value  [#permalink]

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08 Jul 2018, 05:18
00:00

Difficulty:

25% (medium)

Question Stats:

81% (00:55) correct 19% (01:36) wrong based on 16 sessions

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If $$y^{-2} + 2y^{-1} -15 = 0$$, which of the following could be the value of y?

A. $$3$$

B. $$\frac{1}{5}$$

C $$\frac{-1}{5}$$

D. $$\frac{-1}{3}$$

E. $$-5$$

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Re: If y^(-2) + 2y^(-1) -15 = 0, which of the following could be the value  [#permalink]

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08 Jul 2018, 05:26
Bunuel wrote:
If $$y^{-2} + 2y^{-1} -15 = 0$$, which of the following could be the value of y?

A. $$3$$

B. $$\frac{1}{5}$$

C $$\frac{-1}{5}$$

D. $$\frac{-1}{3}$$

E. $$-5$$

Let $$y^{-1}=x$$

So, $$y^{-2} + 2y^{-1} -15 = 0$$
Or, $$x^2+2x-15=0$$
Or, x=-5 or x=3

1. x=-5, or, $$y^{-1}=-5$$ or, $$y=\frac{-1}{5}$$
2. x=3,or, $$y^{-1}=3$$ or, $$y=\frac{1}{3}$$

Among given options, correct answer is (C)[/quote]
https://gmatclub.com/forum/if-y-2-2y-1- ... 69804.html
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Re: If y^(-2) + 2y^(-1) -15 = 0, which of the following could be the value &nbs [#permalink] 08 Jul 2018, 05:26
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