AJUTOR!Multumesc anticipat

Gf intersect. OX <=> f (x)=0 <=> -x+4=0 <=> -x= -4 <=> x=4 => {A (4,0)}
Gf intersect. OY <=> f (0) = 4 => {B (0,-4)}
OA=OB=4 u => triunghiul OAB isoscel