crack math 2 ( q# 25, is it an error or??)

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niktacal82

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If x^2 - 2 x y + Y^2 = 2 and xy=2, which of the following is true?

1) x=y
2) x= y+1
3) x= y-1
4)x=y+2
5)x= y-2

So the answer in crack exp is 1)x=y . Is this wrong or I don't see it? howcome xy=2 and x=y??

The explanation says (x-y)^2= 2-xy ---> (x-y)^2= 0 --> x=y
 
I think xy=2 and x=y if x and y are square root of 2.

Anyway I don't understand it either.
 
the answer is definitely not a)

even if u plug it in, it doesnt make sense...

the only way x = y will make sense is if the

x^2 - 2 xy + y^2 = 0 (not 2)
 
If x^2 - 2 x y + Y^2 = 2 and xy=2, which of the following is true?

1) x=y
2) x= y+1
3) x= y-1
4)x=y+2
5)x= y-2

So the answer in crack exp is 1)x=y . Is this wrong or I don't see it? howcome xy=2 and x=y??

The explanation says (x-y)^2= 2-xy ---> (x-y)^2= 0 --> x=y
x^2 - 2xy + y^2 = 2

Since x^2 - 2xy + y^2 is the same as (x-y)^2, you have:

(x-y)^2 = 2

None of them are correct.

My guess is that they either meant to write x^2 - xy + y^2 = 2, or x^2 - 2xy + y^2 = 2 - xy. Either of those 2 would give the answer x = y.
 
Yea they are but its good practice. Its a shame they don't improve the solutions because it can be a great resource and its clearly needed my almost all who are taking the test this year.
E-mail them the mistake. They pay you for it. They were really nice I make like 50 bux
 
I agree~ with Streetwolf.

Think about it, if x=y then -2xy is the same as -2y^2, and if you add Y^2 - 2y^2 + X^2 and x=y then it is the same as 2y^2 - 2y^2 which obviously equals zero not 2. Therfore it is obviously wrong.
 
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