Is X + Y = 1?

[Strive_Do IT]

If X^2 + Y^2 = 1, is X + Y = 1?

(1) XY = 0
(2) Y = 0

Pls provide explanation on how to work this problem out.

Thanks,

[krusta80]

If X^2 + Y^2 = 1, is X + Y = 1?

(1) XY = 0
(2) Y = 0

Pls provide explanation on how to work this problem out.

Thanks,

Wow, I'm out of it today...

1. If XY = 0, then either x or y is zero. Both can't be zero though, since X^2 + Y^2 = 1.

So, either x^2 = 1 or y^2 = 1, which allows for x or y to be -1 or 1. So, X+Y can be either 1 or -1.

INSUFFICIENT

2. We already covered this in part 1. If y = 0 then x can be 1 or -1.

INSUFFICIENT

E

[lsr]

Answer is E.

Krusta,
1^2=1 and (-1)^2 = 1.

For xy=0; x+y=1 or x+y=-1

[CrackXam]

Another vote for E.

[ken_english]

E for me ..another one of those +/- classics

[nikiforos]

Another vote for E