r
a
n
g
e
2
0
v
a
r
i
a
b
l
e
s
i
n
(
x
-
a
)
(
x
-
b
)
(
x
-
c
)
(
x
-
d
)
a
6
b
5
c
4
d
1
a
s
y
m
p
t
o
t
e
s