Question

Va rog sa-mi aratati macar un exemplu

Answer 1

a.  (n-1)! /(n-3)! <= 20 <=> (n-3)!·(n-2)!·(n-1) /(n-3)! <= 20 <=> (n-2)!·(n-1) <= 20 =>

daca n < 2 => (n-2)! nu exista (nu are valori naturale) => n >= 2 ;pentru n=2 =>

0!·1! <= 20 <=> 1 <= 20 ,este solutie ;

n=3 => 1!·2! <= 20 <=> 2 <= 20 ,este solutie ;

n=4 => 2!·3! <= 20 <=> 12 <= 20 ,este solutie ;

n=5 => 3!·4! <= 20 <=> 120 <= 20 ,care nu convine .

Asadar n∈{2;3;4} .

b.  16n! /(n-1)! > 5n! /(n-2)! <=> daca n < 2 => (n-2)! nu exista (nu are valori naturale) => n >= 2 ;pentru n=2 => 32 > 10 ,care este solutie ;

n=3 => 96/4 > 30 <=> 96 > 120 ,care nu convine .

Asadar n∈{2} .