Byju's Answer
Standard XII
Mathematics
Summation by Sigma Method
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
)
No worries! We‘ve got your back. Try BYJU‘S free classes today!
B
2
(
n
+
1
r
+
1
)
No worries! We‘ve got your back. Try BYJU‘S free classes today!
C
2
(
n
+
2
r
)
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
(
n
+
2
r
)
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
Open in App
Solution
The correct option is
D
(
n
+
2
r
)
n
C
r
+
n
C
r
−
1
+
n
C
r
−
1
+
n
C
r
−
2
=
(
n
C
r
+
n
C
r
−
1
)
+
(
n
C
r
−
1
+
n
C
r
−
2
)
=
n
+
1
C
r
+
n
+
1
C
r
−
1
=
n
+
2
C
r
This comes from the property that
n
C
r
−
1
+
n
C
r
=
n
+
1
C
r
Suggest Corrections
0
Similar questions
Q.
For
2
≤
r
≤
n
,
(
n
r
)
+
2
(
n
r
−
1
)
+
(
n
r
+
2
)
=
Q.
If
n
C
r
−
1
+
n
+
1
C
r
−
1
+
n
+
2
C
r
−
1
+
.
.
.
.
.
.
.
+
2
n
C
r
−
1
,
=
2
n
+
1
C
r
2
−
132
−
n
C
r
, then the value of
r
Q.
If
n
≥
r
−
1
and
n
C
r
−
1
+
n
+
1
C
r
−
1
+
n
+
2
C
r
−
1
+
.
.
.
.
+
2
n
C
r
−
1
=
2
n
+
1
C
r
2
−
182
−
n
C
r
then the least possible value of
n
is
Q.
Assertion :
∑
n
r
=
0
r
(
n
C
r
)
2
=
n
(
2
n
−
1
C
n
−
1
)
Reason:
∑
n
r
=
0
(
n
C
r
)
2
=
2
n
C
n
Q.
Column - I
Column - II
(A)
∑
n
r
=
1
r
.
n
C
r
is equal to
(P)
(
n
+
2
)
.2
n
−
1
(B)
∑
n
+
1
r
=
1
r
.
n
C
r
−
1
is equal to
(Q)
(
n
+
1
)
.
2
n
C
n
(C)
∑
n
r
=
0
(
2
r
+
1
)
.
n
C
r
is equal to
(R)
(
n
+
1
)
.2
n
(D)
∑
n
r
=
0
(
2
r
+
1
)
.
(
n
C
r
)
2
is equal to
(S)
n
.2
n
−
1
View More
Related Videos
Summation by Sigma Method
MATHEMATICS
Watch in App
Explore more
Summation by Sigma Method
Standard XII Mathematics
Solve
Textbooks
Question Papers
Install app