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IF x(X-5)(X+2)=0 is x negative? 1.x sq.2-7x is not equal to

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IF x(X-5)(X+2)=0 is x negative? 1.x sq.2-7x is not equal to [#permalink] New post 10 May 2009, 11:09
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IF x(X-5)(X+2)=0 is x negative?
1.x sq.2-7x is not equal to 0
2. x2-2x-15 is not equal to O.

Please help. OA is [img]c[img]
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Re: is x negative..please help [#permalink] New post 12 May 2009, 03:47
IF x(X-5)(X+2)=0 is x negative?
1.x^2-7x is not equal to 0
2. x^2-2x-15 is not equal to O.
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Re: is x negative..please help [#permalink] New post 12 May 2009, 04:07
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vaivish1723 wrote:
If x(x-5)(x+2)=0 is x negative?
1.x^2-7x is not equal to 0
2. x^2-2x-15 is not equal to O.


1. x^2-7x is not equal to 0
x(x-7) is not equal to 0. so x is neither 0 nor 7. insuff.

2. x^2-2x-15 is not equal to O.[/quote]
x^2 - 2x - 15 is not equal to 0.
(x^2 - 5x + 3x - 15) is not equal to 0.
(x - 5) (x + 3) is not equal to 0.
x is neither 5 nor -3.

Togather x must be -2 to have x (x-5) (x+2) = 0. suff.

C.
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Re: is x negative..please help [#permalink] New post 14 May 2009, 13:06
vaivish1723 wrote:
IF x(X-5)(X+2)=0 is x negative?
1.x sq.2-7x is not equal to 0
2. x2-2x-15 is not equal to O.

Please help. OA is [img]c[img]


Fact: x(x-5)(x+2)=0
Question:( x<0 )?

Interpret fact to get that x=0,5 or -2, in the first 2 cases we have NO, in the last one we have a YES.

So we need more data.

(1) x*sqrt(7x) != 0 (correct me if I read this wrong)
This means that x != 0 & that sqrt(7x) != 0. I don't think this is an Official question (GRRRR) or a very
poorly formulate one, but we can't test x=-2 as the square root of a negative number is a complex number... So if we can use complex numbers, insufficient, and if we aren't allowed to take the square root of a negative number, sufficient, as X can only be 5. But I'm going to go with Insufficient.

(2) x^2 - 2x - 15 != 0
Factorize the quadratic,
x^2 - 5x + 3x - 15 != 0
x(x - 5) + 3(x - 5) != 0
(x-5)(x+3) !=0
So X can't be 5 or -3, but it can still be 0 or -2. Insufficient.

(1&2)
From original equation: x=0,5,-2
1 eliminates 0
2 eliminates 5
Only x=-2 remains

Final Answer, C.
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Re: is x negative..please help   [#permalink] 14 May 2009, 13:06
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