Chapter 10: Problem 43
Let \(f(x)\) have derivatives through order \(n\) at \(x=a .\) Show that the Taylor polynomial of order \(n\) and its first \(n\) derivatives have the same values that \(f\) and its first \(n\) derivatives have at \(x=a\) .
Short Answer
Expert verified
The Taylor polynomial and its derivatives match \( f(x) \) and its derivatives at \( x = a \).
Step by step solution
01
Understanding the Taylor Polynomial
The Taylor polynomial of order \( n \) for a function \( f(x) \) at \( x = a \) is given by \( P_n(x) = f(a) + f'(a)(x-a) + \frac{f''(a)}{2!}(x-a)^2 + \ldots + \frac{f^{(n)}(a)}{n!}(x-a)^n \). This polynomial approximates \( f(x) \) near \( x = a \).
02
Evaluating the Taylor Polynomial at x = a
Evaluate \( P_n(a) \), which becomes \( f(a) + f'(a)(a-a) + \frac{f''(a)}{2!}(a-a)^2 + \ldots + \frac{f^{(n)}(a)}{n!}(a-a)^n \). All terms involving \((x-a)\) vanish, leaving \( P_n(a) = f(a) \).
03
Deriving the First Derivative of Taylor Polynomial
Find the first derivative of \( P_n(x) \). For example, if \( P_n(x) = f(a) + f'(a)(x-a) + \frac{f''(a)}{2!}(x-a)^2 + \ldots + \frac{f^{(n)}(a)}{n!}(x-a)^n \), then \( P_n'(x) = f'(a) + f''(a)(x-a) + \frac{f^{(3)}(a)}{2!}(x-a)^2 + \ldots + \frac{f^{(n)}(a)}{(n-1)!}(x-a)^{n-1} \).
04
Evaluating the First Derivative at x = a
Set \( x = a \) for the first derivative. This gives \( P_n'(a) = f'(a) \) as all terms involving \((x-a)\) again vanish. Thus, the first derivative of the Taylor polynomial at \( x = a \) matches the first derivative of \( f \) at \( x = a \).
05
Generalizing to Higher Derivatives
Similarly, by repeatedly differentiating and setting \( x = a \), we find that each successive derivative \( P_n^{(k)}(a) = f^{(k)}(a) \) for \( k = 2, 3, \ldots, n \), as all terms involving \((x-a)\) vanish after differentiation.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivatives
Derivatives are fundamental in calculus, assisting us in understanding the rate at which a function changes. When we discuss a derivative, commonly denoted as \( f'(x) \), it represents the slope of the tangent line to the curve of \( f(x) \) at a given point. More generally, derivatives can be seen as a tool for assessing how a small change in \( x \) impacts the value of \( f(x) \).
Here are some key points about derivatives:
Here are some key points about derivatives:
- They provide a measure of sensitivity in a function's output relative to changing inputs.
- The first derivative gives the slope of the function, while higher-order derivatives can reveal more about the function’s behavior.
- At a point of tangency, the derivative equals the slope of the tangent line, illustrating an instantaneous rate of change.
Function Approximation
Function approximation is the process of finding a function that closely represents the behavior of a more complicated or unknown function. Taylor polynomials are a powerful method for function approximation, particularly for smooth functions at a certain point.
Why use Taylor polynomials for approximation?
Why use Taylor polynomials for approximation?
- They provide a polynomial of finite degree that approximates a function, making calculations easier than using an infinite series.
- These polynomials can be evaluated by knowing the derivatives of the function at a specific point, usually making it computationally simpler.
- Taylor polynomials are highly accurate near the point of expansion, \( x = a \).
Higher Order Derivatives
Higher order derivatives extend beyond the first derivative, providing deeper insights into a function's behavior. The \( n \)-th derivative of a function is denoted by \( f^{(n)}(x) \).
Here are some points to remember about higher order derivatives:
Here are some points to remember about higher order derivatives:
- They help in understanding a function's curvature and concavity, by analyzing how the slope of the slope changes.
- The second derivative \( f''(x) \) informs us about the acceleration of the function, while the third and subsequent derivatives provide additional layers of analysis.
- In Taylor polynomials, higher order derivatives are crucial for determining the coefficients of the polynomial terms, ensuring the polynomial matches the rate of change to a required order.