5/9 of 729 find the sum
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Answer:
Given, first term of a GP is a=729
and 7
th
term, a
7
=ar
6
=64
⇒729r
6
=64
⇒r
6
=(
3
2
)
6
⇒r=
3
2
= Common ratio
Therefore, a
1
+a
2
+a
3
+a
4
+a
5
+a
6
+a
7
= Sum of the first seven terms
=
1−r
a(1−r
7
)
=
1−
3
2
729{1−(
3
2
)
7
}
=
729×3
729×3
(729×3−128)
=2059
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