Taylor and Maclaurin series are powerful tools for representing functions as infinite sums. They allow us to approximate complex functions using simpler polynomial expressions, making calculations and analysis easier in many areas of math and science.
These series are essential for understanding function behavior, estimating values, and solving differential equations. By learning about their properties, convergence, and applications, we gain valuable insights into the nature of mathematical functions and their representations.
Taylor and Maclaurin Series
Defining Taylor and Maclaurin Series
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Substituting into the Maclaurin series formula:
ex=1+x+2!x2+3!x3+...
Manipulating Taylor Series
Taylor series can be manipulated using standard algebraic operations (addition, subtraction, multiplication, division)
When adding or subtracting Taylor series, add or subtract the corresponding coefficients of like terms
When multiplying Taylor series, use the Cauchy product formula to multiply the coefficients
Dividing Taylor series involves finding the reciprocal series and then multiplying
Composition of Taylor series can be performed by substituting one series into another
These manipulations allow for deriving Taylor series of more complex functions from known series (exponential, trigonometric, logarithmic)
Maclaurin Series for Common Functions
Exponential and Logarithmic Functions
The Maclaurin series for the exponential function ex is:
ex=1+x+2!x2+3!x3+...
The Maclaurin series for the natural logarithm function ln(1+x) is:
ln(1+x)=x−2x2+3x3−4x4+...
Valid for −1<x≤1
The Maclaurin series for the exponential function ax (where a>0 and a=1) is:
ax=1+(lna)x+2!(lna)2x2+3!(lna)3x3+...
The Maclaurin series for the logarithmic function loga(1+x) (where a>0 and a=1) is:
loga(1+x)=lna1(x−2x2+3x3−4x4+...)
Valid for −1<x≤1
Trigonometric Functions
The Maclaurin series for the sine function sin(x) is:
sin(x)=x−3!x3+5!x5−7!x7+...
The Maclaurin series for the cosine function cos(x) is:
cos(x)=1−2!x2+4!x4−6!x6+...
The Maclaurin series for the tangent function tan(x) is:
tan(x)=x+3x3+152x5+31517x7+...
Valid for −2π<x<2π
The Maclaurin series for the hyperbolic sine function sinh(x) is:
sinh(x)=x+3!x3+5!x5+7!x7+...
The Maclaurin series for the hyperbolic cosine function cosh(x) is:
cosh(x)=1+2!x2+4!x4+6!x6+...
Function Approximation with Taylor Polynomials
Constructing Taylor Polynomials
A Taylor polynomial is a finite sum of terms from a Taylor series, used to approximate a function near a given point
The nth-degree Taylor polynomial for a function f(x) centered at a is denoted by Pn(x) and is given by the formula:
Pn(x)=f(a)+f′(a)(x−a)+2!f′′(a)(x−a)2+...+n!f(n)(a)(x−a)n
To approximate a function using a Taylor polynomial, choose an appropriate degree n and center point a based on the desired accuracy and region of interest
Compute the derivatives of the function up to the nth order and evaluate them at the center point a
Substitute the values of the derivatives into the formula for the nth-degree Taylor polynomial
The resulting polynomial Pn(x) approximates the function f(x) near the point a, with accuracy increasing as n increases
Example: Construct a 3rd-degree Taylor polynomial for f(x)=sin(x) centered at a=0 (Maclaurin polynomial)
P3(x)=x−3!x3
Error Analysis and Bounds
The error in approximating a function f(x) by its nth-degree Taylor polynomial Pn(x) is given by the remainder term Rn(x)
The Taylor remainder theorem provides an upper bound for the absolute value of the error:
∣Rn(x)∣≤(n+1)!M∣x−a∣n+1
M is the maximum value of the (n+1)th derivative of f(x) on the interval between a and x
Lagrange error bound: If ∣f(n+1)(x)∣≤M for all x between a and x0, then
∣Rn(x0)∣≤(n+1)!M∣x0−a∣n+1
Cauchy error bound: If ∣f(n+1)(x)∣≤M for all x within a radius of R from a, then
∣Rn(x)∣≤(n+1)!MRn+1
Valid for ∣x−a∣<R
These error bounds help determine the accuracy of Taylor polynomial approximations and guide the choice of the degree n