Explicație pas cu pas:
8/x²€N <=> x²€D8 in N =>x²€{1,2,4,8} =>
x€{+-1,+-V2,+-2,+-2V2}
x€Z => x€{+-1,+-2}
x²+5/x²+1€N <=> x²+1|x²+5
x²+1|x²+5
x²+1|x²+1
=>x²+1|x²+5-x²-1 => x²+1|4 => x²+1€D4 in N =>
x²+1€{1,2,4} =>
x²€{0,1,3} => x€{0,+-1,+-V3}
x€Z => x€{0,+-1}
2x²+3/3x²-8€N <=>
3x²-8|2x²+3=>3x²-8|6x²+9
3x²-8|3x²-8=>3x²-8|6x²-16
=>3x²-8|6x²+9-6x²+16 =>3x²-8|25 =>3x²-8€D25 in Z =>
3x²-8€{-25,-5,-1,1,5,25} =>
3x²€{-17,3,7,9,13,33}
=> 3x²€{3,7,9,13,33} am luat doar valorile pozitive pt ca x²>=0
=> x²€{1,7/3,3,13/3,11} =>x€{+-1,+-V7/V3,+-V13/V3,+-V11,+-V3}
x€Z => x€{+-1}
