Salut!
Răspuns: d ✅
[tex]\bf \frac{35}{3n+1} \in N=>\frac{35}{3n+1}\:este\:numar\:natural=>\bf 3n+1 \in D_3_5 => 3n + 1 \in \{1; 5; 7; 35\}[/tex]
[tex]\bf 3n+1=1 \\\bf 3n = 1-1\\\bf 3n = 0\\\bf 3n = 0 : 3\\\bf x = 0 \in N[/tex]
[tex]\bf 3n+1=5\\\bf 3n = 5-1\\\bf 3n = 4\\\bf n=\frac{4}{3} \not\in N[/tex]
[tex]\bf 3n+1=7\\\bf 3n=7-1\\\bf 3n=6\\\bf = 6 : 3\\\bf n = 2 \in N[/tex]
[tex]\bf 3n+1=35\\\bf 3n = 35-1\\\bf 3n = 34\\\bf n = \frac{34}{3}\not\in N[/tex]
[tex]\bf \big A = \{n\in N| \frac{35}{3n+1}\in N \}[/tex]
[tex]\bf \big A =\{0; 2\}[/tex]
[tex]\bf card \:A = 2 ==>d[/tex]☑️
