Answer:
Here,
3
,
(
−
6
)
,
12
,
(
−
24
)
,
...
is the geometric sequn.
w
h
e
r
e
,
1
s
t
t
e
r
m
=
a
1
=
3
and
common ratio
r
=
−
6
3
=
12
−
6
=
−
24
12
=
−
2
and
S
9
=
?
⇒
n
=
9
We know that,
The sum of first n term of Geometric series is :
S
n
=
a
1
(
r
n
−
1
)
r
−
1
Putting ,
a
1
=
3
,
r
=
−
2
and
n
=
9
S
9
=
3
[
(
−
2
)
9
−
1
]
(
−
2
)
−
1
∴
S
9
=
3
[
−
512
−
1
]
−
3
⇒
S
9
=
3
(
−
513
)
−
3
⇒
S
9
=
513
Explanation: