Let f: → R →(0, ∞) be strictly increasing function such that lim_x → ∞ (f(7 x))/(f(x))=1. Then, the value of lim_x → ∞[(f(5 x))/(f(x))-1] is equal to

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