Math Problem Statement

The function f(x)=ln(2x3)f\left(x\right)=\ln\left(2x-3\right) has the inverse function gg Find g(1) g^{\prime}\left(1\right)\text{ }in two ways.

Solution

To find g(1)g'(1), where g(x)g(x) is the inverse function of f(x)=ln(2x3)f(x) = \ln(2x - 3), we can use two methods. Let’s proceed step by step:


1. Using the Relationship Between a Function and Its Inverse

The derivative of an inverse function satisfies: g(a)=1f(g(a)),g'(a) = \frac{1}{f'(g(a))}, where f(g(a))=af(g(a)) = a.

Step 1.1: Determine g(1)g(1)

Since g(x)g(x) is the inverse of f(x)f(x), we solve f(x)=1f(x) = 1 to find the value of g(1)g(1): f(x)=ln(2x3)=1.f(x) = \ln(2x - 3) = 1. Exponentiating both sides: 2x3=e12x=e+3x=e+32.2x - 3 = e^1 \quad \Rightarrow \quad 2x = e + 3 \quad \Rightarrow \quad x = \frac{e + 3}{2}. Thus, g(1)=e+32g(1) = \frac{e + 3}{2}.

Step 1.2: Compute f(x)f'(x)

The derivative of f(x)f(x) is: f(x)=ddxln(2x3)=12x32=22x3.f'(x) = \frac{d}{dx} \ln(2x - 3) = \frac{1}{2x - 3} \cdot 2 = \frac{2}{2x - 3}.

Step 1.3: Evaluate f(g(1))f'(g(1))

Substitute g(1)=e+32g(1) = \frac{e + 3}{2} into f(x)f'(x): f(g(1))=22(e+32)3=2e+33=2e.f'(g(1)) = \frac{2}{2\left(\frac{e + 3}{2}\right) - 3} = \frac{2}{e + 3 - 3} = \frac{2}{e}.

Step 1.4: Compute g(1)g'(1)

Using g(1)=1f(g(1))g'(1) = \frac{1}{f'(g(1))}: g(1)=12e=e2.g'(1) = \frac{1}{\frac{2}{e}} = \frac{e}{2}.


2. Directly Differentiating the Inverse Relationship

The functions f(x)f(x) and g(x)g(x) satisfy: f(g(x))=x.f(g(x)) = x. Differentiating both sides with respect to xx: f(g(x))g(x)=1.f'(g(x)) \cdot g'(x) = 1. Thus: g(x)=1f(g(x)).g'(x) = \frac{1}{f'(g(x))}.

Step 2.1: Evaluate g(1)g(1)

As determined earlier, g(1)=e+32g(1) = \frac{e + 3}{2}.

Step 2.2: Compute f(g(1))f'(g(1))

From earlier: f(g(1))=2e.f'(g(1)) = \frac{2}{e}.

Step 2.3: Compute g(1)g'(1)

g(1)=1f(g(1))=12e=e2.g'(1) = \frac{1}{f'(g(1))} = \frac{1}{\frac{2}{e}} = \frac{e}{2}.


Final Answer:

g(1)=e2.g'(1) = \frac{e}{2}.


Do you want me to expand further on any step or concept?
Here are 5 follow-up questions related to this problem:

  1. What is the geometric interpretation of the derivative of an inverse function?
  2. How does the chain rule apply in differentiating f(g(x))=xf(g(x)) = x?
  3. What are the conditions for the existence of an inverse function for f(x)f(x)?
  4. How do we find the domain and range of f(x)=ln(2x3)f(x) = \ln(2x - 3)?
  5. Can you compute g(x)g'(x) for a general xx instead of at a specific point?

Tip: Remember that the derivative of an inverse function at a point can be interpreted as the reciprocal of the slope of the original function at the corresponding point.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Inverse Functions
Derivatives
Logarithmic Functions
Differentiation of Inverse Functions

Formulas

g'(a) = 1 / f'(g(a))
f'(x) = d/dx [ln(2x - 3)] = 2 / (2x - 3)

Theorems

Inverse Function Derivative Theorem

Suitable Grade Level

Grades 11-12