Example 2.  Consider the function  [Graphics:Images/TaylorPolyMod_gr_107.gif].  
2 (a).  Find the terms up to  [Graphics:Images/TaylorPolyMod_gr_108.gif]  in the Maclaurin series for  f[x].
Solution 2 (a).

2 (a).  Find the terms up to  [Graphics:../Images/TaylorPolyMod_gr_111.gif]  in the Maclaurin series for  f[x].

[Graphics:../Images/TaylorPolyMod_gr_112.gif]


[Graphics:../Images/TaylorPolyMod_gr_113.gif]

Remark.  If you just find the "Series" it will include a "Big [Graphics:../Images/TaylorPolyMod_gr_114.gif]"  term, which cannot be used in either evaluations or graphing, we eliminate it with the command "Normal."  The "Big [Graphics:../Images/TaylorPolyMod_gr_115.gif]  term lets us know the power of x in the "remainder.

[Graphics:../Images/TaylorPolyMod_gr_116.gif]

[Graphics:../Images/TaylorPolyMod_gr_117.gif]


[Graphics:../Images/TaylorPolyMod_gr_118.gif]

[Graphics:../Images/TaylorPolyMod_gr_119.gif]

Aside.  Of course the "full" Maclaurin series has an infinite number of terms.  Mathematica is capable of finding sums of infinite series.  

The following is just for fun !

There are two ways to get infinite sums, the old way and the new way.

[Graphics:../Images/TaylorPolyMod_gr_120.gif]
[Graphics:../Images/TaylorPolyMod_gr_121.gif]

[Graphics:../Images/TaylorPolyMod_gr_122.gif]
[Graphics:../Images/TaylorPolyMod_gr_123.gif]

The "symbolic" command is:

[Graphics:../Images/TaylorPolyMod_gr_124.gif]
[Graphics:../Images/TaylorPolyMod_gr_125.gif]

Now graph f[x] and the Maclaurin polynomial s[x] over the interval [-2, 2].  

[Graphics:../Images/TaylorPolyMod_gr_126.gif]

[Graphics:../Images/TaylorPolyMod_gr_127.gif]

[Graphics:../Images/TaylorPolyMod_gr_128.gif]

The curves are distinct, but this is only evident if we look at them over a larger interval.

[Graphics:../Images/TaylorPolyMod_gr_129.gif]

[Graphics:../Images/TaylorPolyMod_gr_130.gif]

[Graphics:../Images/TaylorPolyMod_gr_131.gif]

Background for part 2 (b).  Use the fact that the series is "alternating" to investigate the error for the Maclaurin polynomial of degree n = 10 over the interval  [-2.0, 2.0].  

Now look closely at the "error" when the series is used to approximate the function. How close are were the two curves in part (a) ?

[Graphics:../Images/TaylorPolyMod_gr_132.gif]

[Graphics:../Images/TaylorPolyMod_gr_133.gif]

[Graphics:../Images/TaylorPolyMod_gr_134.gif]

This series is "very nice" because it is alternating, and for that reason the error bound is the magnitude of the "next non-zero term" in the series.

[Graphics:../Images/TaylorPolyMod_gr_135.gif]
[Graphics:../Images/TaylorPolyMod_gr_136.gif]

[Graphics:../Images/TaylorPolyMod_gr_137.gif]
[Graphics:../Images/TaylorPolyMod_gr_138.gif]

The error bound for the entire interval  [-2.0, 2.0] is

[Graphics:../Images/TaylorPolyMod_gr_139.gif]
[Graphics:../Images/TaylorPolyMod_gr_140.gif]

[Graphics:../Images/TaylorPolyMod_gr_141.gif]
[Graphics:../Images/TaylorPolyMod_gr_142.gif]

[Graphics:../Images/TaylorPolyMod_gr_143.gif]
[Graphics:../Images/TaylorPolyMod_gr_144.gif]

This estimate is "conservative" and is a little larger than the "actual" maximum error which occurred at   [Graphics:../Images/TaylorPolyMod_gr_145.gif]  

[Graphics:../Images/TaylorPolyMod_gr_146.gif]

[Graphics:../Images/TaylorPolyMod_gr_147.gif]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(c) John H. Mathews 2004