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Consider function [tex]$f$[/tex] and function [tex]$g$[/tex].

[tex]\[
\begin{array}{l}
f(x)=\ln x \\
g(x)=-5 \ln x
\end{array}
\][/tex]

How does the graph of function [tex]$g$[/tex] compare with the graph of function [tex]$f$[/tex]?

A. The graphs of both functions have a vertical asymptote of [tex]$x=0$[/tex].
B. Unlike the graph of function [tex]$f$[/tex], the graph of function [tex]$g$[/tex] has a [tex]$y$[/tex]-intercept.
C. Unlike the graph of function [tex]$f$[/tex], the graph of function [tex]$g$[/tex] has a domain of [tex]$\{x \mid -5\ \textless \ x\ \textless \ \infty\}$[/tex].
D. Unlike the graph of function [tex]$f$[/tex], the graph of function [tex]$g$[/tex] decreases as [tex]$x$[/tex] increases.
E. The graph of function [tex]$g$[/tex] is the graph of function [tex]$f$[/tex] reflected over the [tex]$x$[/tex]-axis and vertically stretched by a factor of 5.


Sagot :

To analyze the behavior and transformation of the functions [tex]\( f(x) = \ln x \)[/tex] and [tex]\( g(x) = -5 \ln x \)[/tex], let's break down the properties and compare the two functions in various aspects:

1. Vertical Asymptote:
- For the function [tex]\( f(x) = \ln x \)[/tex], there is a vertical asymptote at [tex]\( x = 0 \)[/tex]. This is because the natural logarithm function tends to [tex]\(-\infty\)[/tex] as [tex]\( x \)[/tex] approaches 0 from the positive side.
- For the function [tex]\( g(x) = -5 \ln x \)[/tex], the vertical asymptote remains at [tex]\( x = 0 \)[/tex]. This is because the transformation applied to [tex]\( f(x) \)[/tex] does not affect the vertical asymptote.

Therefore, the graph of both functions [tex]\( f \)[/tex] and [tex]\( g \)[/tex] have a vertical asymptote at [tex]\( x = 0 \)[/tex].

2. Monotonicity:
- The function [tex]\( f(x) = \ln x \)[/tex] is an increasing function, meaning as [tex]\( x \)[/tex] increases, [tex]\( \ln x \)[/tex] also increases.
- The function [tex]\( g(x) = -5 \ln x \)[/tex] is a decreasing function. This is because multiplying the natural logarithm by [tex]\(-5\)[/tex] reverses the direction of the slope, causing it to decrease as [tex]\( x \)[/tex] increases.

So, unlike the graph of function [tex]\( f \)[/tex], the graph of [tex]\( g \)[/tex] decreases as [tex]\( x \)[/tex] increases.

3. Transformation:
- The function [tex]\( g(x) = -5 \ln x \)[/tex] can be considered as a transformation of [tex]\( f(x) = \ln x \)[/tex]. Specifically, [tex]\( g(x) \)[/tex] is obtained by reflecting [tex]\( f(x) \)[/tex] over the [tex]\( x \)[/tex]-axis and then stretching it vertically by a factor of 5.

The graph of function [tex]\( g \)[/tex] is the graph of function [tex]\( f \)[/tex] reflected over the [tex]\( x \)[/tex]-axis and vertically stretched by a factor of 5.

4. Domain:
- Both functions [tex]\( f(x) = \ln x \)[/tex] and [tex]\( g(x) = -5 \ln x \)[/tex] have the same domain: [tex]\( x > 0 \)[/tex]. Therefore, the statements claiming different domains for [tex]\( f \)[/tex] and [tex]\( g \)[/tex] are incorrect.

The correct domain for both functions is [tex]\( \{ x \mid x > 0 \} \)[/tex].

Summary:
- The vertical asymptote for both [tex]\( f(x) \)[/tex] and [tex]\( g(x) \)[/tex] is [tex]\( x = 0 \)[/tex].
- [tex]\( f(x) \)[/tex] is an increasing function, whereas [tex]\( g(x) \)[/tex] is a decreasing function.
- The graph of [tex]\( g(x) \)[/tex] is the reflection of [tex]\( f(x) \)[/tex] over the [tex]\( x \)[/tex]-axis and a vertical stretch by a factor of 5.

Thus, the correct descriptive statements for comparing [tex]\( f \)[/tex] and [tex]\( g \)[/tex] are:
1. The graphs of both functions have a vertical asymptote of [tex]\( x = 0 \)[/tex].
2. Unlike the graph of function [tex]\( f \)[/tex], the graph of function [tex]\( g \)[/tex] decreases as [tex]\( x \)[/tex] increases.
3. The graph of function [tex]\( g \)[/tex] is the graph of function [tex]\( f \)[/tex] reflected over the [tex]\( x \)[/tex]-axis and vertically stretched by a factor of 5.