
cos x 5
X
N
n50
ð21Þ
n
x
2n
ð2nÞ!
5 1 2
x
2
2!
1
x
4
6 !
2
x
8
8 !
1 ?
tan
21
x 5
X
N
n50
ð21Þ
n
x
2n11
2n 1 1
5 x 2
x
3
3
1
x
5
5
2
x
7
7
1 ?
lnð1 1 xÞ5
X
N
k50
ð21Þ
k
x
k11
k 1 1
5 x 2
x
2
2
1
x
3
3
2
x
4
4
1 ?
ð11xÞ
α
5 1 1
X
N
k51
αðα 2 1Þ...ðα 2 k 1 1Þ
k !
x
k
5 1 1 αx 1
αðα 2 1Þ
2!
x
2
1
αðα 2 1Þðα 2 2Þ
3!
x
3
1 ?
5.33 Continuous Fourier Series
For a function with period T, a continuous Fourier series can be expressed as
f ðtÞ5 a
0
1
X
N
k51
a
k
cosðkw
0
tÞ1 b
k
sinðkw
0
tÞ
The unknown Fourier coefficients a
0
, a
k
, and b
k
can be computed as
a
0
5
1
T
ð
T
0
f ðtÞdt
Thus, a
0
can be interpreted as the “average” function value between the period
interval ½0; T.
a
k
5
2
T
0
@
1
A
ð
T
0
f ðtÞcosðkw
0
tÞdt
a
2k
ðhence a
k
is an ‘‘even’’ functionÞ
b
k
5
2
T
0
@
1
A
ð
T
0
f ðtÞsinðkw
0
tÞd