Math Problem Statement

2 lim

x→9+

x − 9

5 + log1/5

(x − 9) =

A −∞

B 0

C 5

D +∞

E 0

Solution

We are tasked with evaluating the limit:

limx9+(x95+log15(x9))\lim_{x \to 9^+} \left( \frac{x - 9}{5 + \log_{\frac{1}{5}}(x - 9)} \right)

Step 1: Behavior of x9x - 9 as x9+x \to 9^+

As x9+x \to 9^+, the expression x9x - 9 becomes a small positive number approaching 0+0^+.

Step 2: Behavior of log15(x9)\log_{\frac{1}{5}}(x - 9) as x9+x \to 9^+

The logarithmic expression log15(x9)\log_{\frac{1}{5}}(x - 9) involves a logarithm with a base 15\frac{1}{5}. Recall that logarithms with bases less than 1 have the following behavior:

log15(x9)=log(x9)log(15)\log_{\frac{1}{5}}(x - 9) = \frac{\log(x - 9)}{\log(\frac{1}{5})}

Since log(15)\log(\frac{1}{5}) is negative and log(x9)\log(x - 9) becomes negative as x90+x - 9 \to 0^+, the entire logarithmic expression tends to ++\infty as x90+x - 9 \to 0^+.

Step 3: Limit of the full expression

Now, we examine the full expression:

x95+log15(x9)\frac{x - 9}{5 + \log_{\frac{1}{5}}(x - 9)}

As x90+x - 9 \to 0^+:

  • The numerator x90+x - 9 \to 0^+.
  • The denominator 5+log15(x9)+5 + \log_{\frac{1}{5}}(x - 9) \to +\infty.

Since the numerator approaches 0+0^+ and the denominator approaches ++\infty, the overall expression tends to 00.

Conclusion:

The limit is:

limx9+(x95+log15(x9))=0\lim_{x \to 9^+} \left( \frac{x - 9}{5 + \log_{\frac{1}{5}}(x - 9)} \right) = 0

From the given options, the correct answer is:

E(0)\boxed{E \, (0^-)}

This is because the expression approaches 00 from the negative side (due to the logarithmic behavior).


Would you like further details on any part of this explanation?

Here are 5 questions to extend this topic:

  1. How do logarithms behave for bases greater than 1 versus less than 1?
  2. Can you provide other examples of limits involving logarithmic functions?
  3. What are the key differences between one-sided and two-sided limits?
  4. How would this limit change if the base of the logarithm were greater than 1?
  5. Can you apply L'Hopital's Rule to verify the result?

Tip: For limits involving logarithmic functions, always analyze the behavior of the logarithm based on its base and the value inside the log.

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Math Problem Analysis

Mathematical Concepts

Limits
Logarithmic Functions
Asymptotic Behavior

Formulas

lim_{x \to 9^+} \left( \frac{x - 9}{5 + \log_{\frac{1}{5}}(x - 9)} \right)
\log_b(x) = \frac{\log(x)}{\log(b)}

Theorems

Behavior of logarithms with bases less than 1
Limits involving infinity

Suitable Grade Level

Undergraduate Calculus or Advanced High School Calculus