5. Find the sum of last 20 coefficients in the expansion of (1 + x)^39
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Answer:
i hope this answer is correct
Step-by-step explanation:
(1+x)
59
=
59
C
0
+
59
C
1
x+
59
C
2
x
2
+....
59
C
59
x
59
Substituting x=1, we get
2
59
=
59
C
0
+
59
C
1
+
59
C
2
+....
59
C
59
2
59
=2[
59
C
0
+
59
C
1
+
59
C
2
+....
59
C
28
]+
59
C
29
+
59
C
30
2
59
=2[
59
C
0
+
59
C
1
+
59
C
2
+....
59
C
28
+
59
C
29
]
Since
59
C
30
=
59
C
29
2
59
=2[
59
C
59
+
59
C
58
+
59
C
57
+....
59
C
31
+
59
C
30
]
2
59
=2(requiredsum)
Required sum =2
58
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