(n-1)!/(n-3)!=20, tentukan nilai n!

Faktorial

( (n – 1)! ) / ( (n – 3)! ) = 20
( (n – 1)(n – 2)(n – 3)! ) / (n – 3)! = 20
(n – 1)(n – 2) = 20
n² – 3n + 2 = 20
n² – 3n – 18 = 0
(n – 6)(n + 3) = 0
n = 6 v n = -3
ambil positif

n = 6