Question

resolva as equações b)an,2=9 An,1 c)an,2+an-1,2+An-2,2=20

Answer 1

Boa tarde Leonardo

b) 

(n!)/((n - 2)!) = 9*(n!)/((n - 1)!)

1/(n - 2)! = 9/(n - 1)!

(n - 1)! = 9*(n - 2)!

(n - 1)*(n - 2)! = 9*(n - 2)!

n - 1 = 9
n = 10

c)

n!/(n - 1)! + (n - 1)!/(n - 3)! + (n - 2)!/(n - 4)! 

(n - 3) (n - 2) + (n - 1) (n - 2) + n = 20 

n² - 5n + 6 + n² - 3n + 2 + n = 20

2n² - 7n + 8 = 20

2n² - 7n - 12 = 0

delta
d² = 49 + 96 = 145
d = √145 

n1 = (7 + √145)/4 
n2 = (7 - √145)/4