(x+y)/(1+xy)>-1
(x+y).>-(1+xy)
x+y>-1-xy
x+y+xy+1>0
(x+xy)+(y+1>0
x((1+y)+(y+1)>0
(y+1)(x+1)>0 evident fiecare paranteza e pozitiva
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(x+y)/(1+xy)<1
(x+y)<1+xy
x+y-1-xy<0
(x-xy)+(y-1)<0
-x(y-1)+(y-1)<0
(y-1)(1-x)<0 Evident pt ca y-1<0 si 1-x>0
