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GMATPrep equation problem

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by netigen » Mon May 12, 2008 1:15 am
Help me get this one right.

I thought we can solve for XY using both the equations if we subtract one equation from another we get

x^2 = x or x=1 and hence, y=2

OA is E
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by amitansu » Mon May 12, 2008 1:19 am
Netigen, you are right.
Ans should be C.


Amit
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by akshatsingh » Mon May 12, 2008 9:03 pm
x^2 = x doesnt mean x = 1.

it means x(x-1) = 0
=> x=0 or x=1

Clearly a unique xy cannot be found out using these values of x.


I believe answer should be E.
Aks
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by netigen » Mon May 12, 2008 9:39 pm
I knew I was doing something stupid 8), thanks for pointing it out.
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by gabriel » Tue May 13, 2008 11:28 am
akshatsingh wrote:x^2 = x doesnt mean x = 1.

it means x(x-1) = 0
=> x=0 or x=1

Clearly a unique xy cannot be found out using these values of x.


I believe answer should be E.
This is a very common mistake committed in DS. We have to remember any quadratic equation will have 2 roots. So never ever stop after you find one value for x if there is a term x^2 in the equation.

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