Chapter 8: Infinite Sequences and Series
Section 8.5: Taylor Series
Example 8.5.2
Show that R^n+1x for fx=ex goes to zero as n→∞, establishing that f has a Maclaurin series.
Find the terms of that series.
Solution
Mathematical Solution
The Taylor-series remainder for fx=ex is
R^n+1x=exn+1!xn+1
For each fixed x, R^n+1x→0, as suggested by Figure 8.5.2(a) where n is controlled by the slider.
As n→∞, R^n+1x→0 but the limit is not uniform in x. As n increases, the interval on which the remainder gets close to zero increases to the right.
n= =
Figure 8.5.2(a) Slider-controlled graph of R^n+1
In the limit as n→∞, the interval on which the remainder approaches zero becomes the whole real line.
The Maclaurin series is fx=ex=∑n=0∞xnn! because fnx=ex and fn0=1 for n=0,1,….
Maple Solution
The expression for R^n+1
Write R=… Context Panel: Assign Name
R=ⅇx xn+1n+1!→assign
Show that R^n+1→0 as n→∞
Calculus palette: Limit template Context Panel: Evaluate and Display Inline
limn→∞R = 0
Obtain the Maclaurin series
Write the exponential function, being sure to use a Maple template or palette for "e".
Context Panel: Series≻Formal Power Series Complete the dialog as per Figure 8.5.2(b).
Figure 8.5.2(b) Formal Power Series dialogc
ⅇx→formal series∑n=0∞xnn!
Obtain the Maclaurin series from first principles
Write fx=…(Use the correct "e"!) Context Panel: Assign Function
fx=ⅇx→assign as functionf
Expression palette: Summation template
Context Panel: 2-D Math≻Convert To≻Inert Form
Context Panel: Evaluate and Display Inline
∑n=0∞fn0n!xn = ∑n=0∞xnn!
Note: The symbol for the nth-derivative can be typed, or it can be obtained as the template fnx in the Calculus palette.
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