Respuesta :

valdana350

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

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