Math Problem Statement

Find the degree 2 Taylor polynomial for the function ln(-2x-5) centered at x =-5.

Solution

To find the degree 2 Taylor polynomial of the function f(x)=ln(2x5)f(x) = \ln(-2x - 5) centered at x=5x = -5, we will follow these steps:

Step 1: Function and its Derivatives

We need the function and its first two derivatives evaluated at x=5x = -5.

Function at x=5x = -5:

f(x)=ln(2x5)f(x) = \ln(-2x - 5) Substitute x=5x = -5: f(5)=ln(2(5)5)=ln(105)=ln(5)f(-5) = \ln(-2(-5) - 5) = \ln(10 - 5) = \ln(5)

First derivative:

The derivative of f(x)=ln(2x5)f(x) = \ln(-2x - 5) using the chain rule is: f(x)=22x5f'(x) = \frac{-2}{-2x - 5} Substitute x=5x = -5: f(5)=22(5)5=2105=25f'(-5) = \frac{-2}{-2(-5) - 5} = \frac{-2}{10 - 5} = \frac{-2}{5}

Second derivative:

Differentiate f(x)=22x5f'(x) = \frac{-2}{-2x - 5} again using the quotient rule: f(x)=(2)(2)(2x5)2=4(2x5)2f''(x) = \frac{(-2)(-2)}{(-2x - 5)^2} = \frac{4}{(-2x - 5)^2} Substitute x=5x = -5: f(5)=4(105)2=425f''(-5) = \frac{4}{(10 - 5)^2} = \frac{4}{25}

Step 2: Taylor Polynomial Formula

The formula for the degree 2 Taylor polynomial is: P2(x)=f(a)+f(a)(xa)+f(a)2(xa)2P_2(x) = f(a) + f'(a)(x - a) + \frac{f''(a)}{2}(x - a)^2 Here, a=5a = -5, and the values we calculated are: f(5)=ln(5),f(5)=25,f(5)=425f(-5) = \ln(5), \quad f'(-5) = \frac{-2}{5}, \quad f''(-5) = \frac{4}{25} Substitute into the Taylor polynomial: P2(x)=ln(5)+25(x+5)+425(x+5)22P_2(x) = \ln(5) + \frac{-2}{5}(x + 5) + \frac{4}{25} \cdot \frac{(x + 5)^2}{2} Simplifying: P2(x)=ln(5)25(x+5)+225(x+5)2P_2(x) = \ln(5) - \frac{2}{5}(x + 5) + \frac{2}{25}(x + 5)^2

Thus, the degree 2 Taylor polynomial for ln(2x5)\ln(-2x - 5) centered at x=5x = -5 is: P2(x)=ln(5)25(x+5)+225(x+5)2P_2(x) = \ln(5) - \frac{2}{5}(x + 5) + \frac{2}{25}(x + 5)^2

Would you like more details or have any questions?

Here are some related questions:

  1. How do we determine the degree of a Taylor polynomial?
  2. Why is the Taylor series centered around a specific point, and how is this point chosen?
  3. How can we approximate natural logarithmic functions using Taylor polynomials?
  4. What happens if we use a higher-degree Taylor polynomial for this function?
  5. How can we generalize Taylor series expansions for more complex functions?

Tip: Always double-check the function and its derivatives at the chosen center to avoid small calculation errors in Taylor series.

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Math Problem Analysis

Mathematical Concepts

Calculus
Taylor Polynomial
Logarithmic Functions

Formulas

Taylor Polynomial: P_n(x) = f(a) + f'(a)(x - a) + f''(a)/2!(x - a)^2 + ...
Derivative of ln(-2x - 5): f'(x) = -2 / (-2x - 5)
Second Derivative: f''(x) = 4 / (-2x - 5)^2

Theorems

Taylor Series Expansion
Chain Rule
Quotient Rule

Suitable Grade Level

Undergraduate Calculus