if (-a) in = 1 where n is even then a =
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0
Answer:
Correct option is
D
none of these
Solution -
we know that,
n
C
0
+
n
C
1
+
n
C
2
+
n
C
3
+−−−−−
n
C
n
=2
n
Also
n
C
0
−
n
C
1
+
n
C
2
−
n
C
3
+−−−−−−+
n
C
n
=0
Subtract -
2(
n
C
1
+
n
C
3
+
n
C
5
+−−−−−
n
C
n−1
)=2
n
1!(n−1)!
n!
+
3!(n−3)!
n!
+−−−−−−−−
(n−1)!1!
n!
=2
n−1
1!(n−1)!
1
+
3!(n−3)!
1
+−−−−−−
(n−1)!1!
1
=
n!
2
n−1
D is correct.
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