Question

Sa se rezolve ecuațiile :

Answer 1

==========  Conditii necesare :  x≥3 ; n≥3

Answer 2

a.  x! /(x-3)! =2·x <=> x! /x·(x-3)! =2 <=> (x-1)! /(x-3)! =2 <=> (x-3)!·(x-2)·(x-1) /(x-3)! =2 <=> (x-2)·(x-1) =2 <=> x-2 < x-1 => x-2=1 si x-1=2 <=>  x=3 .

b.  (n-1)! /(n-3)! -n! /(n-1)! =79 <=> (n-2)·(n-1) -n=79 <=>n² -n-2n +2-n=79 <=> n² -4n+2=79 <=> n² -4n -77=0 <=> n=7 sau n=11 => n=11 este solutie .