Mult¸imea numerelor naturale:
N = {0, 1, 2, . . . , n}
N* = {1, 2, . . . , n}
Multimea numerelor intregi
Z = {..., −n,... , −2, −1, 0, 1, 2, . . . , n,...}
Multimea numerelor rationale
Q =
{a/ b
| a, b ∈ Z, b ≠ 0}
Multimea numerelor irationale
I=R-Q
Deci:
-3∈Z
2,79∈Q
√11∈ I
pi ∈ I
5pi ∈ I
-3,2(7)∈ Q
