Chapter 10: Problem 9
Find the Taylor polynomials of degree \(n\) approximating the functions for \(x\) near \(0 .\) (Assume \(p\) is a constant. \()\) $$\frac{1}{\sqrt{1+x}}, \quad n=2,3,4$$
Short Answer
Expert verified
Taylor polynomials: Degree 2: \(1 - \frac{1}{2}x + \frac{3}{4}x^2\), Degree 3: \(1 - \frac{1}{2}x + \frac{3}{4}x^2 - \frac{15}{8}x^3\), Degree 4: \(1 - \frac{1}{2}x + \frac{3}{4}x^2 - \frac{15}{8}x^3 + \frac{105}{16}x^4\).
Step by step solution
01
Recall Taylor Series Formula
The Taylor series expansion of a function \(f(x)\) around \(x = a\) is given by: \[f(x) = f(a) + f'(a)(x-a) + \frac{f''(a)}{2!}(x-a)^2 + \frac{f^{(3)}(a)}{3!}(x-a)^3 + \cdots\]For this exercise, \(a=0\) and we need the expansions up to \(n=4\).
02
Derive the Function and Its Derivatives
The function given is \(f(x) = \frac{1}{\sqrt{1+x}}\). First, calculate the derivatives at \(x = 0\):- \(f(x) = (1+x)^{-1/2}\).- \(f'(x) = -\frac{1}{2}(1+x)^{-3/2}\).- \(f''(x) = \frac{3}{4}(1+x)^{-5/2}\).- \(f^{(3)}(x) = -\frac{15}{8}(1+x)^{-7/2}\).- \(f^{(4)}(x) = \frac{105}{16}(1+x)^{-9/2}\).Evaluate these derivatives at \(x=0\).
03
Simplify the Derivatives at x = 0
Evaluate the derivatives calculated in the previous step at \(x=0\):- \(f(0) = 1\).- \(f'(0) = -\frac{1}{2}\).- \(f''(0) = \frac{3}{4}\).- \(f^{(3)}(0) = -\frac{15}{8}\).- \(f^{(4)}(0) = \frac{105}{16}\).
04
Construct Taylor Polynomials
Using the derivatives at \(x=0\), construct the Taylor polynomials for different degree values:- Degree 2: \[T_2(x) = 1 - \frac{1}{2}x + \frac{3}{4}x^2\]- Degree 3: \[T_3(x) = 1 - \frac{1}{2}x + \frac{3}{4}x^2 - \frac{15}{8}x^3\]- Degree 4: \[T_4(x) = 1 - \frac{1}{2}x + \frac{3}{4}x^2 - \frac{15}{8}x^3 + \frac{105}{16}x^4\]
05
Present the Final Polynomials
The final Taylor polynomials approximating \(\frac{1}{\sqrt{1+x}}\) near \(x=0\) are:- Degree 2: \(T_2(x) = 1 - \frac{1}{2}x + \frac{3}{4}x^2\).- Degree 3: \(T_3(x) = 1 - \frac{1}{2}x + \frac{3}{4}x^2 - \frac{15}{8}x^3\).- Degree 4: \(T_4(x) = 1 - \frac{1}{2}x + \frac{3}{4}x^2 - \frac{15}{8}x^3 + \frac{105}{16}x^4\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Taylor Series
The Taylor series is a powerful tool in calculus for approximating functions. It allows a function to be expressed as an infinite sum of terms. Each term is calculated from the derivatives of the function at a given point. The formula for a Taylor series expansion of a function \(f(x)\) around the value \(x = a\) is:\[f(x) = f(a) + f'(a)(x-a) + \frac{f''(a)}{2!}(x-a)^2 + \frac{f^{(3)}(a)}{3!}(x-a)^3 + \cdots\]The series provides an approximation that becomes closer to the real function as more terms are added.
- The point \(a\) is where the series is centered.
- Each term involves higher order derivatives of the function.
- In practical use, only a finite number of terms are computed for a desired degree of accuracy.
Derivatives
A derivative represents the rate at which a function changes at a particular point. It's a central concept in calculus and fundamental to the formation of Taylor series. Calculating derivatives is necessary to determine each polynomial term in a Taylor series.
- The first derivative \(f'(x)\) indicates the slope at any point on the function.
- The second derivative \(f''(x)\) shows the rate of change of the slope.
- Higher-order derivatives, such as third \(f^{(3)}(x)\) and fourth \(f^{(4)}(x)\), provide further information about changes in the function's behavior.
- We determined the derivatives of \(f(x) = \frac{1}{\sqrt{1+x}}\).
- Calculated these derivatives at \(x = 0\) to construct the Taylor polynomial.
- As each derivative is evaluated, it contributes to a specific term in the polynomial.
Polynomial Approximation
Polynomial approximation is an approach used to estimate more complex mathematical functions using simpler polynomials. Taylor polynomials are a type of polynomial approximation derived from the Taylor series. They offer a useful way to get close to the actual values of a function, especially near the point where the series is centered.
- Short polynomial expressions replace a potentially infinite series.
- Each additional term in the Taylor polynomial provides a more accurate approximation.
- For computations or predictions, several terms usually provide enough precision.
- These polynomials approximate the function near \(x = 0\).
- As more terms are added (higher degrees), accuracy improves.
- Taylor polynomials are especially useful when dealing with functions near their center point, \(x = a\).
Mathematical Functions
A mathematical function maps a set of inputs (domain) with corresponding outputs (range). In calculus, functions are the basis for determining behavior over intervals or specific points. A function like \(f(x) = \frac{1}{\sqrt{1+x}}\) reveals how \(f\) changes as \(x\) changes.
- Functions can exhibit complex behavior that requires approximation for analysis.
- Polynomial and Taylor series approximations provide simpler ways to study functions.
- They help calculate values over an input domain and understand local behavior around specific values.
- This involves understanding how the original function behaves in this region.
- The calculated Taylor polynomials give insight into predicted values close to the center.
- This foundational tool in calculus supports deeper exploration of changes in rate and extent in mathematical functions.