f
(
x
)
x
g
(
x
)
-
1
c
o
s
(
x
)
D
x
(
f
(
x
)
g
(
x
)
)
=
g
(
x
)
′
f
(
x
)
-
f
(
x
)
′
g
(
x
)
2
g
(
x
)
=
1
2
x
-
1
c
o
s
(
x
)
-
x
-
1
1
-
2
x
2
-
1
c
o
s
(
x
)
=
x
1
-
2
x
2
-
1
c
o
s
(
x
)
+
1
2
x
-
1
c
o
s
(
x
)