Question

calcule
(n+1)!
----------- = 12
(n-1)!

Answer 1

(n+1)!

----------- = 12

(n-1)!

(n+1).n.(n-1)!

-------------------- = 12

(n-1)!

(n+1).n = 12

n² +n -12 = 0

∆=1+48= 49 => √∆ = 7

n' = -b+√∆/2

n' = -1+7/2 = 6/2 = 3✓