M15#37 : Retired Discussions [Locked]
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# M15#37

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Joined: 30 May 2009
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22 Jun 2009, 18:44
1. b = |c| . This stmt tells us 2 things. First, b is positive. Second, $$b^2 = c^2.$$

$$b^2 = c^2$$
=> $$b^2 - c^2$$ = 0
=> $$a^2 - b^2$$ = 0
=> |a| = |b|

So INSUFF. Because we cannot for sure say that a=|b| because a can be a negative number as well.

2. b = |a|. This stmt is clearly insufficient, because this does not guarantee again that a = |b|. We dont know if a is positive or negative.

Combining (1) and (2) gives

|a| = |b| and b=|a|. We still cannot for sure say that a=|b|.
Because take values a=b=2. Then a=|b|
But take values a=-2, b=2. Then $$a<>|b|$$

Re: M15#37   [#permalink] 22 Jun 2009, 18:44
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# M15#37

Moderator: Bunuel

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