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Byju's Answer
Standard XI
Mathematics
Number of Terms in Binomial Expansion
For 2 ≤ r ≤ n...
Question
For
2
≤
r
≤
n
,
(
n
r
)
+
2
(
n
r
−
1
)
+
(
n
r
−
2
)
is equal to
A
(
n
+
1
r
−
1
)
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B
(
n
+
1
r
+
1
)
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C
2
(
n
+
2
r
)
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D
(
n
+
2
r
)
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Solution
The correct option is
D
(
n
+
2
r
)
(
n
r
)
+
2
(
n
r
−
1
)
+
(
n
r
−
2
)
=
[
(
n
r
)
+
(
n
r
−
1
)
]
[
(
n
r
−
1
)
+
(
n
r
−
2
)
]
=
(
n
+
1
r
)
+
(
n
+
1
r
−
1
)
=
(
n
+
2
r
)
[
∵
n
C
r
+
n
C
r
−
1
=
n
+
1
C
r
]
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0
Similar questions
Q.
For
2
≤
r
≤
n
,
(
n
+
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r
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+
(
n
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−
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r
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is equal to-
Q.
The value of
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Q.
Prove that if
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and
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are positive integers
n
r
−
n
(
n
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1
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+
n
(
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−
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2
!
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(
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Q.
The value of
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→
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∑
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r
+
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.
.
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is
Q.
For
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≤
r
≤
n
,
(
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r
)
+
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(
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n
r
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is equal to
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