Show that there are no points of the graph of y = log; x where the tangent line is horizontal.

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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**Problem:**

Show that there are no points of the graph of \( y = \log_5 x \) where the tangent line is horizontal.

**Solution:**

To determine where the tangent line to the graph of \( y = \log_5 x \) is horizontal, we need to find the derivative \( y' \) and set it to zero.

1. **Find the Derivative:**

   The derivative of \( y = \log_5 x \) with respect to \( x \) is:
   \[
   y' = \frac{d}{dx}(\log_5 x) = \frac{1}{x \ln 5}
   \]

2. **Set the Derivative to Zero:**

   For the tangent line to be horizontal, the derivative must be zero:
   \[
   \frac{1}{x \ln 5} = 0
   \]

   However, \( \frac{1}{x \ln 5} \) is never zero for any real value of \( x \). Thus, there are no points where the derivative is zero and therefore no points where the tangent line is horizontal.

**Conclusion:**

The graph of \( y = \log_5 x \) has no points where the tangent line is horizontal.
Transcribed Image Text:**Problem:** Show that there are no points of the graph of \( y = \log_5 x \) where the tangent line is horizontal. **Solution:** To determine where the tangent line to the graph of \( y = \log_5 x \) is horizontal, we need to find the derivative \( y' \) and set it to zero. 1. **Find the Derivative:** The derivative of \( y = \log_5 x \) with respect to \( x \) is: \[ y' = \frac{d}{dx}(\log_5 x) = \frac{1}{x \ln 5} \] 2. **Set the Derivative to Zero:** For the tangent line to be horizontal, the derivative must be zero: \[ \frac{1}{x \ln 5} = 0 \] However, \( \frac{1}{x \ln 5} \) is never zero for any real value of \( x \). Thus, there are no points where the derivative is zero and therefore no points where the tangent line is horizontal. **Conclusion:** The graph of \( y = \log_5 x \) has no points where the tangent line is horizontal.
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