n
u
m
b
e
r
o
f
s
a
m
p
l
e
p
o
i
n
t
s
4
0
g
r
a
p
h
b
a
c
k
g
r
o
u
n
d
c
o
l
o
r
3
p
o
i
n
t
s
i
z
e
2
.
4
π
≈
2
9
1
0
=
2
.
9
0
0
0
0