Question:

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

Updated On: Nov 19, 2024
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  • \(\frac{7}{5}\)
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The Correct Option is B

Solution and Explanation

Given:

\[ \lim_{x \to \infty} \frac{f(7x)}{f(x)} = 1 \]

Since \( f \) is strictly increasing, we have:

\[ f(x) < f(5x) < f(7x) \]

This implies:

\[ \lim_{x \to \infty} \frac{f(5x)}{f(x)} = 1 \]

Then:

\[ \lim_{x \to \infty} \left[ \frac{f(5x)}{f(x)} - 1 \right] = 1 - 1 = 0 \]

Thus, the answer is: 0.

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