If x2 + y2 = 1, is x + y = 1? (1) xy = 0 (2) y = 0

Question

If x2 + y2 = 1, is x + y = 1?
(1) xy = 0
(2) y = 0

atletikos · Answer

IMO E

Even combined, x can be either 1 or -1, Insuff

HG · Answer

IMO C

Here is why

x+y = 1 
or 
(x+y)^2 = 1

x^2 + y^2 + 2xy = 1

1+2xy = 1 ( x^2+y^2 = 1 - given in Q)

or the question is asking is xy =0?

1 - Suff
2- Suff

selvae · Answer

IMO E

x2 + y2 = 1 deriving from Q (x+y)^2 = 1+2xy

1) xy = 0; so x+y = +/- 1
2) y=0; x2 = 1; x+y = +/- 1

vivektripathi · Answer

Value of X could be -1 or +1 hence E OA isE

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