Question

Resolva:
n!/2!(n-2)! = 10

Answer 1

(n ×(n-1)×(n-2)! )÷ 2 × 1× (n-2)! = 10
(n² - n) ÷2 =10
n²-n = 20
n²-n-20 = 0
Δ= 1²- 4×1× (-20) = 1 + 80 =81

n'= (1 + √81) ÷ 2 = (1 + 9) ÷2 = 10÷2=5
n"= (1-√81) ÷2 = (1-9) ÷2 = -8÷2 = -4