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Cat este:  (n-3)factorial supra (n-5)factorial = 6 

Răspuns :

(n-3)!/(n-5)!=6
(n-3)(n-4)(n-5)!/(n-5)!=6
(n-3)(n-4)=6
n²-7n+12-6=0
n²-7n+6=0
Δ=b²-4ac=49-24=25
n1,2=(-b+/-√Δ)/2a
n1=(7-5)/2=1
n2=(7+5)/2=6