x;y;z inv.prop cu 1/3; 6/90 ;1/6
x,y, z d.p cu inversele numerelor, deci cu 3; 90/6 ; 6
x y z d.p cu 3;15;6
x/3=y/15=z/6=k
x=3k
y=15k
z=6k
xy-yz+xz=540
45k²-90k²+18k²
-27k²=540
-k²=20
k²=-20
k∉R⇒x,y,z∉R⇒x;y;z∉N⊂R
k=+-i√20=+- i*2√5∈C\R
dimpotriva, pt
xy+yz+xz=540
45k²+90k²+18k²=540
153k²=540
k²=180/51=60/17
k=+-√(60/17)∉N⇒x,y,z∉N