N= multimea numerelor naturale={0,1,2,3,...}
Z= multimea numerelor intregi={...,-3,-2,-1,0,1,2,3,...}
R= multima numrelor reale, care pot fi si numere intregi si numere cu zecimale adica virgula={...,-3 ,-2 ,-1 ,0 ,1 , 1,02 , 1, 2, 2, 3,...}
Q=numere rationale adica numere care au radicali= { √2, √2/3,...}