3 Si los números $x_1$, $x_2$, ..., $x_n$ pertenecen al intervalo $\left( \frac{1}{4},1 \right)$, demuestra la desigualdad: $\log _{x_1} {\left(x_2-\frac{1}{4} \right)} + \log _{x_2} {\left(x_3-\frac{1}{4} \right)}+ ... + \log _{x_{n-1}} {\left(x_n-\frac{1}{4} \right)} + \log _{x_n} {\left(x_1-\frac{1}{4} \right)} \geq 2n$