(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