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difficult problem solving Q

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difficult problem solving Q

by ccassel » Thu Mar 24, 2011 2:28 pm
Hi all,

Would anyoneone be able to explain this answer?

If x does not = 0 and x = root(4xy-4y^2), then, in terms of y, x =

A. 2y
B. y
C. y/2
D. -4y^2/1-4y
E. -2y

Thanks,
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by ccassel » Thu Mar 24, 2011 2:31 pm
The answer is A but I don't know how to get there. Thanks,
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by srcc25anu » Thu Mar 24, 2011 3:48 pm
x = sqrt(4xy-4y^2)
squaring both sides: x^2 = 4xy - 4y^2
taking them all to left hand side and equating to zero we get: x^2-4xy+4y^2 = 0 or (x-2y)^2 = 0
since x-2y=0; x=2y
hence A
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by ccassel » Thu Mar 24, 2011 4:06 pm
Great, thanks!
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by Night reader » Thu Mar 24, 2011 4:38 pm
answer choice A

If x=2y then x = root(8y^2-4y^2), then, in terms of y, x = root(4y^2), x=|2y|

If x=-2y then x = root(4y *-2y -4y^2), then, in terms of y, x = root(-12y^2), since the root of negative value cannot be defined for x=-2y, x=|2y| --> x=2y

srcc25anu wrote:x = sqrt(4xy-4y^2)
squaring both sides: x^2 = 4xy - 4y^2
taking them all to left hand side and equating to zero we get: x^2-4xy+4y^2 = 0 or (x-2y)^2 = 0
since x-2y=0; x=2y
hence A
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