Question

C(n+1,n-1) = 28,maka nilai n adalah?
a 12
b 10
c 9
d 8
e7

Answer 1

C(n+1, n-1)

= (n+1)! / (n-1)! ((n+1) - (n-1))!
= (n+1)! / (n-1)! (2)!
= (n+1)! / (n-1)! * 2
= (n+1)! / (n-1)! * 2
= (n+1) * (n) * (n-1)! / (n-1)! * 2
= (n + 1)(n) / 2
= (n² + n) / 2

(n² + n) / 2 = 28
n² + n = 28 * 2
n² + n = 56
n² + n - 56 = 0
(n - 7)(n + 8) = 0
n- 7 = 0
n = 7

n + 8 = 0
n = -8

Kita ambil yang n = 7
jadi nilai n = 7