CLASS_11_MATHS_SOLUTIONS_NCERT

Class XI Chapter 9 – Sequences and Series Maths
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a
a
4 3
3a
2 3 35 2 107
5 4
3a
2 3 107 2 323
Hence, the first five terms of the sequence are 3, 11, 35, 107 and 323.
The corresponding series is 3 11 35 107 323 ....
Question 12:
Write the first fiver terms of the following sequence and obtain the corresponding series:
an
1
a1 1, an
, n 2
n
Solution 12:
a
a a n
n
n1
1
1,
n
, 2
a 1
2 2
1
a2
a
a
a
3
a2
1
3 6
a 1
4 24
3
4
5
a4
1
5 120
Hence, the first five terms of the sequence are
The corresponding series is
1 1 1
1, , ,
2 6 24
and
1 1 1 1
1 ...
2 6 24 120
1
120
.
Question 13:
Write the first five terms of the following sequence and obtain the corresponding series:
a a 2, a a 1, n 2
1 2 n n1
Solution 13:
a a 2, a a 1, n 2
1 2 n n1
a3 a21 2 11
a4 a31 11
0
a5 a41 0 1 1
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