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smallsorrow
- Master | Next Rank: 500 Posts
- Posts: 109
- Joined: Mon Sep 08, 2008 12:47 am
(B)
xy = -6 (given) & to find xy(x+y)
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from (1): x-y = 5 => (y+5)*y = -6 => y = -2/-3
then if y = -2 => x =3, then xy(x+y) = -6(1) = -6
but, if y = -3 => x =2, then xy(x+y) = -6(-1) = 6
therefore, (1) alone is not sufficient
from (2): xy^2=18 => -6*y = 18 => y = -3, from this, we get single value for x too, as xy = -6, hence (2) is sufficient
