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What does p equal?

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What does p equal? [#permalink] New post 25 Jun 2012, 10:57
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42% (02:14) correct 58% (01:00) wrong based on 69 sessions
What does p equal?

(1) 2p^2=p^3

(2) p=2\sqrt{p-1}


i went with D, but was wrong

(1) 2p^2=p^3 divided by p^2 --> 2=p - here was the mistake and id like to ask you to shed the light on this - what don't i understand correctly here?
[Reveal] Spoiler: OA
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What does p equal? [#permalink] New post 25 Jun 2012, 11:07
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Galiya wrote:
What does p equal?

(1) 2p^2=p^3
(2) p=2sqrt{p-1}


i went with D, but was wrong

(1) 2p^2=p^3 divided by p^2 --> 2=p - here was the mistake and id like to ask you to shed the light on this - what don't i understand correctly here?


What does p equal?

(1) 2p^2=p^3 --> p^3-2p^2=0 --> p^2(p-2)=0 --> p=0 or p=2. Not sufficient.

(2) p=2\sqrt{p-1} --> p^2=4(p-1) --> p^2-4p+4=0 --> (p-2)^2=0 --> p=2. Sufficient.

Answer: B.

As for your solution: you cannot divide by p^2 since p could be zero and division by zero is not allowed.

Never reduce equation by variable (or expression with variable), if you are not certain that variable (or expression with variable) doesn't equal to zero. We can not divide by zero. So, if you divide (reduce) by p^2 you assume, with no ground for it, that p does not equal to zero thus exclude a possible solution.

Hope it's clear.
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Manager
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Re: What does p equal? [#permalink] New post 25 Jun 2012, 11:14
thank you, Bunuel!sometimes Im really stuck on such a silly things
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Re: What does p equal? [#permalink] New post 30 Jun 2014, 06:39
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Re: What does p equal?   [#permalink] 30 Jun 2014, 06:39
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