(x+1)! /(x+1-2)!=6
(x+1)! /(x-1)!=6
(x-1)!x(x+1)/(x-1)!=6 (se simplifica in fractie (x-1)!)
x(x+1)=6
x^2+x-6=0
a=1
b=1
c=-6
Δ=b^2-4ac
Δ=1+24
Δ=25
[tex] x_{1} = \frac{-b -\sqrt{delta} }{2a}\\\\ x_{1} = \frac{-1-5}{2} \\ x_{1} -3 \\\\ x_{2} \frac{-b+ \sqrt{delta} }{2a} \\ \\ x_{2} = \frac{-1+5}2} \\ x_{2}= 2 [/tex]
