Question

Determinati multimile : A = {n apartine de N* | 21 supra n apartine N} ; B= {n apartine N*- {1} | 35 supra n-1 apartine N} ; C = { n apartine de N | 40 supra 3n+1 apartine de N}

Answer 1

21/n e nr, natural daca n e divizor pt. 21 (adica impartirea se face exact si nu mai avem fractie)
=>A={1, 3, 7, 21}

35/n-1 e natural daca n-1 e divizor pt.35 => n-1=1, n=2, n-1=5, =>n=6, n-1=7, =>n=8, n-1=35=>n=36
=> B={2, 6, 8, 36}
 la fel afli pe C, unde 3n+1 va fi divizor pt 40.

Spor!