Question

determinati cardinalul multimilor:
A={10,20,30,40.50,60,70,80,90}
B={x I 20 mai mic sau egal x < 31}
C={x I x+5=15}
D={x I x numar natural x > 2 si x< 3}

Answer 1

1)... avem ... (9-1)+1 numere , 
       ⇒ card A= 9 ;
2)... de la 20 pana la 31 inclusiv avem ... (31-20)+1=12 ⇒ card B=12 ;
3)... C={10} (pt.ca x+5=15 ⇒x=15-5=10) deci card C= 1 ;
4)... daca 2 < x < 3 ⇒ x= Ф  adica  card D = Ф (multime vida)