Answer:
sum
In the given G.S., we have,
a
=
the
1
s
t
term
=
3
,
& the common ratio
r
=
−
6
3
=
−
2
Hence, the sum
S
n
of its first
n
terms is given by,
S
n
=
a
(
1
−
r
n
)
1
−
r
∴
The Reqd. Sum S_7
=
3
(
1
−
(
−
2
)
7
)
1
−
(
−
2
)
=
3
(
1
+
128
)
3
=
129
