Answer:
x
18
+
63
x
16
y
+
1764
x
14
y
2
+
28812
x
12
y
3
+
302526
x
10
y
4
+
2117682
x
8
y
5
+
9882516
x
6
y
6
+
29647548
x
4
y
7
+
51883209
x
2
y
8
+
40353607
y
9
Explanation:
(
a
+
b
)
n
=
n
∑
k
=
0
n
C
k
⋅
(
a
n
−
k
b
k
)
.
9
∑
k
=
0
9
!
(
9
−
k
)
!
k
!
⋅
(
x
2
)
9
−
k
⋅
(
7
y
)
k
Expand the summation.
9
!
(
9
−
0
)
!
0
!
⋅
(
x
2
)
9
−
0
⋅
(
7
y
)
0
+
9
!
(
9
−
1
)
!
1
!
⋅
(
x
2
)
9
−
1
⋅
(
7
y
)
+
…
+
9
!
(
9
−
9
)
!
9
!
⋅
(
x
2
)
9
−
9
⋅
(
7
y
)
9
Simplify the exponents for each term of the expansion.
1
⋅
(
x
2
)
9
⋅
(
7
y
)
0
+
9
⋅
(
x
2
)
8
⋅
(
7
y
)
+
…
+
1
⋅
(
x
2
)
0
⋅
(
7
y
)
9
Simplify the polynomial result.
x
18
+
63
x
16
y
+
1764
x
14
y
2
+
28812
x
12
y
3
+
302526
x
10
y
4
+
2117682
x
8
y
5
+
9882516
x
6
y
6
+
29647548
x
4
y
7
+
51883209
x
2
y
8
+
40353607
y
9