The sum of first 3 terms of a G.P is 16
and the sum of next three terms is 128.
Find the first term, common ratio and
sum of n terms.
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1
Answer:
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Answered by
1
Answer:
here you go
Step-by-step explanation:
Let a be the first term and r the common ratio of the G.P.
a+ar+ar
2
=16
and, ar
3
+ar
4
+ar
5
=128
a(1+r+r
2
)=16 and, ar
3
(1+r+r
2
)=128
⇒
a(1+r+r
2
)
ar
3
(1+r+r
2
)
=
16
128
⇒r
3
=8
⇒r=2
Putting the value of r, we get, a=
7
16
Therefore,
S
n
=a(
r−1
r
n
−1
)=
7
16
(
2−1
2
n
−1
)=
7
16
(2
n
−1)
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