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value question

by brontobuffy » Mon Jun 30, 2008 7:50 pm
DS question:
What is the value of x?
1. -(x+y)=x-y
2. x+y=2

the answer is statement 1 alone is sufficient. book explains that 1. can be reduced to 2x=0 or x=0.
i don't see how that equation can be reduced to that?? wouldn't it reduce to
-x-y=x-y
-x+y=x+y
__________
-2x=0???

thanks for any help
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Source: — Data Sufficiency |
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by gxliu » Tue Jul 01, 2008 4:54 am
1. -(x+y)=x-y
Can be reduced to -x-y=x-y.
Simplify to -x=x. The only way this can happen is if x=0. Sufficient.
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by fajoni » Tue Jul 01, 2008 4:05 pm
Statement 1 can be reduced to what you and the book stated.

-(X+Y)=X-Y

-X-Y=X-Y (isolating the X on the left side of the equation yields...)

-2X=0, which leads to X=(0/-2) which means X=0

Now isolate the X on the right side...

-X-Y=X-Y

0=2X, which leads to X=(0/2) which means X=0.

It works both ways.

Good luck with the studying!
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