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# What is the value of x^2 – y^2 ?

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Re: What is the value of x^2 – y^2 ? [#permalink]
Fine x^2-y^2 (x+y)(x-y)

1) x+y=2y-1
=> x-y=-1
even if we multiply both => (x+y)(x-y)= -(2y-1)

Not sufficient

2)5x - 5y = 1/(2x + 2y)
=> 5(x-y) =1/(2x + 2y)
=> 5(x-y) *(2x + 2y)=1
=>5(x-y)*2(x+y)=1
> (x-y)(x+y)=1/10

Sufficient

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Re: What is the value of x^2 – y^2 ? [#permalink]
By using statement 1 we can deduce (x+y)(x-y)= (2y-1) ;"Y" is still unknown.

By using statement 2 we can find (x+y)(x-y)= 1/10

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Re: What is the value of x^2 y^2 ? [#permalink]
chipsy wrote:
We need to find x^2 - y^2 = (x-y) (x+y)

(A) x - y = -1 , Not suff.

(B) 5x - 5y = 1/(2x + 2y)

5 (x-y) * 2(x+y) = 1
10 (x-y) (x+y) =1
(x-y) (x+y) = 1/10
Sufficient.