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Mathematics
Mathematics
Problem
If
(
1
+
x
−
2
x
2
)
20
=
∑
r
=
0
80
a
r
x
r
(1 + x - 2x^2)^{20} = \sum_{r=0}^{80} a_r x^r
(
1
+
x
−
2
x
2
)
20
=
∑
r
=
0
80
a
r
x
r
, then find the value of
a
1
+
a
3
+
a
5
+
⋯
+
a
39
a_1 + a_3 + a_5 + \dots + a_{39}
a
1
+
a
3
+
a
5
+
⋯
+
a
39
.
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