Let $f: \rightarrow \mathbb{R} \rightarrow(0, \infty)$ be strictly increasing function such that $\lim _\limits{x \rightarrow \infty} \frac{f(7 x)}{f(x)}=1$. Then, the value of $\lim _\limits{x \rightarrow \infty}\left[\frac{f(5 x)}{f(x)}-1\right]$ is equal to