cos , if
2
2
( )
3,
if
2
k
x
x
x
f x
x
π

≠
= π −
π

=

       at x = 2
π
27 2, if
2
( )
3,
if
2
kx
x
f x
x

≤
= 
>

            at x = 2
28 1, if
( )
cos ,
if
kx
x
f x
x
x
+
≤ π
= 
> π

         at x = π
29 1, if
5
( )
3
5, if
5
kx
x
f x
x
x
+
≤
= 
−
>

         at x = 5
30