Question

Scrieti 2 multimi de forma Dn,n apartine N*,astfel incat:
a)Carinalul luiDn sa fie egal cu 4
D15={1,3,5,15}
D=..................
b)acestea sa aiba exact 2 elemente
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c)Card Dn=3
......................... .repede!!cat mai repede!!dau pct si coroana!!e neaparat!!AJUTATI-MA!!VAA ROGG!!SUNT SINGURA LA CASA SI NU AM PE NIMENI!!AJUTOR!!!!URGENT!!!!PLS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Answer 1

a) Dn este multimea tuturor divizorilor lui n. Stim ca 1 si n insusi vor fi mereu divizori ai lui n. Asa ca deja 2 elemente le stim. Ca sa mai adaugam doua elemente, trebuie doar sa il facem pe n=a*b, unde (a,b)=1, adica a si b sunt prime intre ele, Atunci elementele lui Dn vor fi: 1,a,b,n
De exemplu, 4 si 7 sunt prime intre ele
asa ca o sa aven n=4*7=28
D28={1,4,7,28}
b) daca are exact 2 elemente, inseamna ca le are doar pe 1 si n, deci n este un numar prim. Numarul 11 de exemplu este prim, asa ca:
D11={1.11}
c) Daca avem cardinal 3, din nou stim ca vor fi 1 si n, iar n=a*b in acest caz pentru ca mai e un singur numar, atunci b=a in mod obligatoriu, iar b trebuie sa fie prim. De exemplu a=2 este un numar prim, de unde reiese ca n=4
D4={1.2.4}