Question

Putin ajutor, va rog! (n-7)!/(n-9)!=12 .Determinati n> sau egal decat 9

Answer 1

[(n-7)(n-8)(n-9)!]/(n-9)!=12

n²-15n+56=12
n²-15n+44=0
Δ=b²-4ac= 225-176=49
n₁/n₂=(-b±√Δ)/2a=(15±7)/2
n₁=(15+7)/2=22/2=11≥9
n₂=(15-7)/2=8/2=4(nu este mai mare sau egal decat 9)
S={11}

Answer 2

(n-7)!/(n-9)!=12
(n-8)(n-7)=12
(n-8)(n-7)=3•4
n-8=3=>n=11
n-7=4=>n=11