Chapter 3: Applications of Differentiation
Section 3.3: Taylor Polynomials
Essentials
Taylor's formula states that a suitably well-behaved function can be represented as a sum of a polynomial and a "remainder" term. This is made precise in Theorem 3.3.1.
Theorem 3.3.1 Taylor's Formula
The function f and f′,f″,…,fn (its first n derivatives) are continuous in α,β
fn is differentiable in α,β
Both x and a are in α,β
⇒
There exists a value c in α,β for which the following representation of f holds.
fx
=Pnx+Rnx
=∑k=0nfkak!x−ak+fn+1cn+1!x−an+1
=fa+f′ax−a+f″a2!x−a2+⋯+fnan!x−an+fn+1cn+1!x−an+1
In Theorem 3.3.1, Pnx is a polynomial of degree n, called a Taylor polynomial.
The symbol fka represents the kth derivative of f evaluated at x=a.
By convention, f0 is taken to mean "no derivative," that is, the function f itself.
The expression for the remainder Rnx is the Lagrange form, but there are at least two other forms, one of which is attributed to Cauchy.
In particular, the first-degree Taylor polynomial is P1x=fa+f′ax−a, and the equation y=P1x is the equation of the tangent line at x=a. Thus, any tool that generates the first-degree Taylor polynomial is a tool that likewise returns the equation of the tangent line!
Examples
Example 3.3.1
For fx=ex at x=0, obtain Taylor polynomials of degree 1, 2, and 3.
Graphically compare these polynomials on −4,4.
Use R3x to estimate the largest difference between f and P3 on −1,1.
Find the actual value of the largest difference between f and P3 on −1,1.
Example 3.3.2
With f and P3 as in Example 3.3.1, obtain R3x and use it to estimate the largest difference between f and P3 on −1,1. Hence, obtain the maximum value of R4 = f4c4!x4, which in turn requires finding the maximal value of f4c for −1≤c≤1.
Example 3.3.3
For fx=sinx with a=0 in Taylor's Formula, obtain the general form of Pnx.
Example 3.3.4
At x=3, obtain the equation of the line tangent to the graph of fx=lnx2+3 x+2.
<< Previous Section Table of Contents Next Section >>
© Maplesoft, a division of Waterloo Maple Inc., 2024. All rights reserved. This product is protected by copyright and distributed under licenses restricting its use, copying, distribution, and decompilation.
For more information on Maplesoft products and services, visit www.maplesoft.com
Download Help Document