IX.B. MacLaurin's Polynomials and Taylor's Theory.
© 2000 M. Flashman


Exercises IX.B: Solutions for odd problems 1-7.

In exercises 1-10 , find Pn(x,f(x)) for the specified function and n.

1. f(x) = sin(x) ; n = 7
 
k
f(k)(x)
f(k)(0)
0
sin(x)
0
1
cos(x)
1
2
-sin(x)
0
3
-cos(x)
-1
4
sin(x)
0
5
cos(x)
1
6
-sin(x)
0
7
-cos(x)
-1
So P7(x,sin(x)) =  x - x3/6  +  x 5/120 - x 7/5040.

3. f(x) = sin(2x) ; n = 7
 
k
f(k)(x)
f(k)(0)
0
sin(2x)
0
1
2cos(2x)
2
2
-4sin(2x)
0
3
-8cos(2x)
-8
4
16sin(2x)
0
5
32cos(2x)
32
6
-64sin(2x)
0
7
-128cos(2x)
-128
So P7(x,sin(2x)) =  2x - 8x3/6  +  32x 5/120 -128 x 7/5040
= 2x - 4x3/3  +  4x 5/15 - 8x 7/315.
 

5. f(x) = e 2x ; n = 6 and n = 7
 
k
f(k)(x)
f(k)(0)
0
exp(2x)
1
1
2exp(2x)
2
2
4exp(2x)
4
3
8exp(2x)
8
4
16exp(2x)
16
5
32exp(2x)
32
6
64exp(2x)
64
7
128exp(2x)
-128
So P6(x,exp(2x)) = 1 + 2x + 4x2/2  + 8x3/6 + 16x4/24 + 32x 5/120 + 64x 6/720
and
P7(x,exp(2x)) = 1 + 2x + 4x2/2  + 8x3/6 + 16x4/24 + 32x 5/120 + 64x 6/720 +128 x 7/5040

7. f(x) = ln(1+x) ; n = 4
 
k
f(k)(x)
f(k)(0)
0
ln(1+x)
0
1
1/(1 + x)
 1
2
-1/(1+x)2
 -1
3
2/(1+x)3
 2
4
-6/(1+x)4
 -6
So P4(x,ln(1+x)) =  x - x2/2  + x3/3  - x4/4