CLASS_11_MATHS_SOLUTIONS_NCERT

Class XI Chapter 9 – Sequences and Series Maths
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Question 3:
The 5 th , 8 th and 11 th terms of a G.P. are
Solution 3:
Let a be the first term and r
a a r a r p
51 4
5
........ 1
a a r a r q
81 7
8
........ 2
a a r a r s
111 10
11
........ 3
Dividing equation (2) by (1), we obtain
a r
a r
r
3
7
4
q
p
q
p
....... 4
Dividing equation (3) by (2), we obtain
a r
a r
10
7
r
3
s
q
s
q
Equating the values of
q s
p q
q
2
ps
...... 5
3
r
Thus, the given result is proved.
pq ,
and s , respectively. Show that
2
q
ps
be the common ratio of the G.P. According to the given condition,
obtained in (4) and (5), we obtain
.
Question 4:
The 4 th term of a G.P. is square of its second term, and the first term is
term.
Solution 4:
Let a be the first term and r be the common ratio of the G.P.
a 3
It is known that,
an
a ar r
3 3
4
3
a a r r
1
2
3
ar
n 1
According to the given condition,
3. Determine its 7 th
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