Jika  n!/(n-2)! = 20  maka n =.... ???

Kelas 10 Matematika
Bab Kombinatorik

n ! / (n - 2) ! = 20
n . (n - 1) . (n - 2) ! / (n - 2) ! = 20
n² - n - 20 = 0
(n - 5) (n + 4) = 0
n + 4 = 0
n = -4 (tidak memenuhi karena negatif)

n - 5 = 0
n = 5 (memenuhi)

Maka, n = 5

n=5
5!/(5-2)! = (5×4×3!)/3! = 20