Hi,
This question is meant to be very easy but I am really stuck with the second part. Could an expert please walk me through how you would eliminate choices?
What is the value of (x+y)^2?
i) x+y+1=0
ii) x^{2}+y^{2}=1-2xy
The place I got this question from said the answer is D
THank you!!
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Hi petud,
The "key" to this DS question is your ability to rewrite the given information and the question.
We're asked for the value of (X+Y)^2.
You might recognize this as one of the "Classic Quadratics", so you can rewrite the question to ask "what is the value of X^2 + 2XY + Y^2?"
Fact 1: X+Y+1 - 0
We can rewrite this Fact as....
X + Y = -1
With THAT value, we can now answer the question (by substituting the value into the question): (-1)^2 = 1
Fact 1 is SUFFICIENT
Fact 2: X^2 + Y^2 = 1 - 2XY
Here, we can add 2XY to both sides, which gives us...
X^2 + 2XY + Y^2 = 1
This ALSO answers the question (although you would have to rewrite the question to realize it).
Fact 2 is SUFFICIENT
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
The "key" to this DS question is your ability to rewrite the given information and the question.
We're asked for the value of (X+Y)^2.
You might recognize this as one of the "Classic Quadratics", so you can rewrite the question to ask "what is the value of X^2 + 2XY + Y^2?"
Fact 1: X+Y+1 - 0
We can rewrite this Fact as....
X + Y = -1
With THAT value, we can now answer the question (by substituting the value into the question): (-1)^2 = 1
Fact 1 is SUFFICIENT
Fact 2: X^2 + Y^2 = 1 - 2XY
Here, we can add 2XY to both sides, which gives us...
X^2 + 2XY + Y^2 = 1
This ALSO answers the question (although you would have to rewrite the question to realize it).
Fact 2 is SUFFICIENT
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
