Tentuka nilai n dari (n-1)!/(n+1)!=9

(n-1)! / (n+1)! = 9
Jawab:
(n-1)(n)(n+1)! / (n+1)! = 9
 (n-1)(n) = 9
n²-n-9 = 0
n1 = ( 1+[tex] \sqrt{37} [/tex] ) / 2
n2 = -(1+[tex] \sqrt{37} [/tex] ) / 2