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If xy ≠ 0 and x2y2 – xy = 6, which of the following could be

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If xy ≠ 0 and x2y2 – xy = 6, which of the following could be [#permalink]

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New post 25 Feb 2011, 07:23
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If xy ≠ 0 and x^2*y^2 - xy = 6, which of the following could be y in terms of x?

I. 1/(2x)
II. – 2/x
III. 3/x

A. I only
B. II only
C. I and II
D. I and III
E. II and III
[Reveal] Spoiler: OA

Last edited by Bunuel on 10 Feb 2014, 04:08, edited 3 times in total.
Renamed the topic, edited the question and the OA.
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If xy ≠ 0 and x2y2 – xy = 6, which of the following could be [#permalink]

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naaga wrote:
If xy ≠ 0 and x2y2 – xy = 6, which of the following could be y in terms of x?

I. 1/(2x)
II. – 2/x
III. 3/x


A. I only
B. II only
C. I and II
D. I and III
E. II and III


If xy ≠ 0 and x^2*y^2 - xy = 6, which of the following could be y in terms of x?

I. 1/(2x)
II. - 2/x
III. 3/x

\(x^2*y^2-xy=6\) --> \((xy)^2-xy-6=0\) --> \((xy-3)(xy+2)=0\) --> either \(xy-3=0\) and in this case \(y=\frac{3}{x}\) or \(xy+2=0\) and in this case \(y=-\frac{2}{x}\).

Answer: E.

naaga, please format the questions properly.

P.S. This is your third question for today with incorrect OA.
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Re: how to solve [#permalink]

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New post 25 Feb 2011, 08:35
Fantastic approach. Thanks!

Bunuel wrote:
naaga wrote:
If xy ≠ 0 and x2y2 – xy = 6, which of the following could be y in terms of x?

I. 1/(2x)
II. – 2/x
III. 3/x


A. I only
B. II only
C. I and II
D. I and III
E. II and III


If xy ≠ 0 and x^2*y^2 - xy = 6, which of the following could be y in terms of x?

I. 1/(2x)
II. - 2/x
III. 3/x

x^2*y^2-xy=6 --> (xy)^2-xy-6=0 --> (xy-3)(xy+2)=0 --> either xy-3=0 and in this case y=3/x or xy+2=0 and in this case y=-2/x.

Answer: E.

naaga, please format the questions properly.

P.S. This is your third question for today with incorrect OA.
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Re: If xy ≠ 0 and x2y2 – xy = 6, which of the following could be [#permalink]

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Re: If xy ≠ 0 and x2y2 – xy = 6, which of the following could be [#permalink]

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Hi All,

This question is quirky in that it tests you on math rules and patterns that you probably know, but in ways that you're not used to thinking about...

We're told that neither X nor Y are equal to 0. We're also told that (X^2)(Y^2) - XY = 6. We're asked which of the following COULD be the value of Y in terms of X...

The first interesting thing about this question is the use of the word COULD....that word implies that there's MORE THAN ONE possible solution.
The second interesting thing is that the 'term' (XY) can be factored out of the 'left side' of the equation. Normally, you look to factor our a single variable or number, but here, it's the product of two variables that you can factor out. Doing so gives us...

XY(XY - 1) = 6

While this looks complicated, there's an easy pattern here:

(number)(number - 1) = 6

Can you think of 2 numbers, that differ by 1, that you can multiply to get 6?

You should be thinking 2 and 3... because (3)(3-1) = 6

So XY = 3 is a possible solution. In this case, Y = 3/X. The wording of the prompt makes me think that there should be another solution though, so is there ANOTHER pair of numbers, that differ by 1, that you can multiply together to get 6? Hint: the numbers do NOT have to be positive....

How about -2 and -3....

(-2)(-2-1) = 6

So XY = -2 is another possible solution. In this case, Y = -2/X

There's only one answer that includes both of those solutions...

Final Answer:
[Reveal] Spoiler:
E


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Re: If xy ≠ 0 and x2y2 – xy = 6, which of the following could be [#permalink]

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New post 08 Jul 2015, 20:57
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I tried this in the following way:

Since the values given are of "y", i plugged in these values in the equation for "y".

Starting with 3rd option first which is easier to plug in, x^2(3/x)^2 - x(3/x) = 6 satisfy the equation.

Plugging in y = -2/x in the equation, x^2(-2/x)^2 - x(-2/x) = 6 also satisfy the equation.

plugging in y = 1/(2x) doesn't satisfy the equation, Hence E.

Is my approach correct?
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Re: If xy ≠ 0 and x2y2 – xy = 6, which of the following could be [#permalink]

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New post 09 Jul 2015, 17:43
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Hi ash99,

YES, your method for dealing with this question is just as effective as any of the others (it's essentially a variation on TEST THE ANSWERS). Based on how the the 5 answer choices are designed, once you proved that the third and second Roman Numerals were potential solutions, then you could have stopped working (since none of the answers included all 3 Roman Numerals).

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Re: If xy ≠ 0 and x2y2 – xy = 6, which of the following could be   [#permalink] 09 Jul 2015, 17:43
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If xy ≠ 0 and x2y2 – xy = 6, which of the following could be

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