Determining decreasing sequence For a sequence $x_{n+1}=4x_n-x_{n-1}$, $x_1=4, x_2=15$, show that the sequence $\frac{x_{n+1}}{x_n}$ is decreasing
I know from calculating that $\frac{x_{n+1}}{x_n}-\frac{x_{n}}{x_{n-1}}=\frac{-1}{x_nx_{n-1}}$, but I can't seem to prove that.
Any tips please?

$$x_{n+1}=4x_n-x_{n-1}$$
divide $x_n$ through out
$\dfrac{x_{n+1}}{x_n}=4-\dfrac{x_{n-1}}{x_n}$ 
$\implies \dfrac{x_{n+1}}{x_n} - \dfrac{x_{n}}{x_{n-1}} =4-\dfrac{x_{n-1}}{x_n} - \dfrac{x_{n}}{x_{n-1}} = 4-\dfrac{x_n^2+{x_{n-1}}^2}{x_nx_{n-1}} \le 0$
Because $a^2+b^2\ge 4ab$
