n
3
(
1
+
x
+
2
x
+
3
x
)
(
1
+
2
x
+
4
x
+
6
x
)
(
1
+
3
x
+
6
x
+
9
x
)
=
1
+
x
+
2
2
x
+
3
3
x
+
…
+
1
8
x