Дифференциальные уравнения. Ряды. Богатова С.В. - 106 стр.

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()
22
1
xdxdx0
1
dxxf
1
a
2
0
0
0
π
=
π
π
=
+
π
=
π
=
π
ππ
π
,
()
=
+
π
=
π
=
π
ππ
π
0
0
n
nxdxcosxnxdxcos0
1
nxdxcosxf
1
a
=
π
=
=
=
=
=
=
π
π
0
0
nxdxsin
n
1
n
nxsinx1
nxsin
n
1
v
nxdxcosdv
dxdu
xu
=
+=
π
=
π
=
π
,k2nесли,0
,1k2nесли,
n
2
n
nxcos
n
1
2
0
()
=
+
π
=
π
=
π
π
π
π 0
0
n
nxdxcos
n
1
n
nxcosx1
nxdxsinxf
1
b
=π=+π
π
π
=
π
ncos
n
1
nxsin
n
1
ncos
n
0
2
=
+=
=
.k2nесли,
n
1
,1k2nесли,
n
1
Таким образом, ряд Фурье будет иметь вид
()
+
+++
π
π
= ...
5
x5cos
3
x3cos
1
xcos2
4
xf
222
+++ ...
4
x4sin
3
x3sin
2
x2sin
1
xsin
.