Question

a) An+1,2+Cn,2=26
revolva a equação

Answer 1

An+1,2 + Cn,2=26

(n+1)!/(n+1-2)! + n!/ 2!(n-2)! = 26
(n+1) n (n-1)!/ (n-1)! + n(n-1)(n-2)!/2!(n-2)! = 26
2[(n+1)n] + n(n-1)/2! = 26
2(n²+n) + n² -n/ 2=26
2n²+2n+n²-n=52
3n²+n-52=0

Δ= 1²-4.3(-52)    n= -1 +/-√625/2.3 
Δ= 625               n'= 4  n"= -26/6 (não convém)

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