Math Problem Statement

Let f be the function given by f(x) = ln(x). What is the approximation for ln(3/2) found by using the line tangent to the graph of f at x = 1?

Solution

Let's solve this step by step.

Problem Breakdown:

We are tasked to find an approximation for ln(32)\ln\left(\frac{3}{2}\right) using the tangent line to the function f(x)=ln(x)f(x) = \ln(x) at x=1x = 1. This involves using linear approximation (or the tangent line approximation).

Formula for Linear Approximation:

The equation of the tangent line at x=ax = a is: L(x)=f(a)+f(a)(xa)L(x) = f(a) + f'(a)(x - a)

Here:

  • f(x)=ln(x)f(x) = \ln(x)
  • a=1a = 1
  • The approximation is for x=32x = \frac{3}{2}.

Step 1: Compute f(a)=f(1)f(a) = f(1)

f(1)=ln(1)=0f(1) = \ln(1) = 0


Step 2: Compute f(x)f'(x), the derivative of f(x)=ln(x)f(x) = \ln(x)

f(x)=1xf'(x) = \frac{1}{x} Thus, at x=1x = 1: f(1)=11=1f'(1) = \frac{1}{1} = 1


Step 3: Write the Tangent Line Equation

Using the formula for L(x)L(x): L(x)=f(1)+f(1)(x1)L(x) = f(1) + f'(1)(x - 1) Substituting the values: L(x)=0+1(x1)=x1L(x) = 0 + 1(x - 1) = x - 1


Step 4: Approximate ln(32)\ln\left(\frac{3}{2}\right)

Substitute x=32x = \frac{3}{2} into the tangent line equation L(x)=x1L(x) = x - 1: L(32)=321=12L\left(\frac{3}{2}\right) = \frac{3}{2} - 1 = \frac{1}{2}

Thus, the approximation for ln(32)\ln\left(\frac{3}{2}\right) is: ln(32)12\ln\left(\frac{3}{2}\right) \approx \frac{1}{2}


Final Answer:

12\boxed{\frac{1}{2}}

Let me know if you want details or have questions! 😊


Related Questions:

  1. How do you derive the linear approximation formula for general functions?
  2. What is the exact value of ln(32)\ln\left(\frac{3}{2}\right), and how does it compare to the approximation?
  3. How can the tangent line approximation be used for other values of xx?
  4. What happens to the accuracy of the approximation as xx moves farther from the point of tangency?
  5. How do you compute derivatives of logarithmic functions with different bases?

Tip:

For functions with rapidly changing slopes, the tangent line approximation works best for values of xx very close to the point of tangency!

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Math Problem Analysis

Mathematical Concepts

Logarithmic Functions
Linear Approximation
Tangent Line

Formulas

L(x) = f(a) + f'(a)(x - a)
f'(x) = 1/x

Theorems

Derivative of Natural Logarithm
Linear Approximation Formula

Suitable Grade Level

Grades 10-12