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Help with Quadratic Equations

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by outreach » Mon Mar 08, 2010 12:45 pm
i feel the answer is E. using both u cannot solve the equ

Question is what is the value of (x-y)(x+y)?

option A
x=2y+2

option B
(x-y)(x+1)=1
x^2+x-yx-y=1


combining both
subst value of x from opt A in eqn obt in opt B
(2y+2)^2+2y+2-y(2y+2)-y=1
4y^2+8y+4+2y+2-2y^2-2y=1
solving we get 2 values of y

if option B was (x+y) instead of (x+1) then answer would have been B
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by yossi » Mon Mar 08, 2010 12:49 pm
outreach wrote:i feel the answer is E. using both u cannot solve the equ

Question is what is the value of (x-y)(x+y)?

option A
x=2y+2

option B
(x-y)(x+1)=1
x^2+x-yx-y=1


combining both
subst value of x from opt A in eqn obt in opt B
(2y+2)^2+2y+2-y(2y+2)-y=1
4y^2+8y+4+2y+2-2y^2-2y=1
solving we get 2 values of y

if option B was (x+y) instead of (x+1) then answer would have been B
I think you right! I am using not so great books. They claim the answer to be B as well...

So fratrating to have mistakes in your GMAT books!!!

Thank you very much
Thank you very much
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