Question

If a = 1, r= 2 find S, for the G.P is
a)2n+1
b)2n-1
c)2n
d)2n-2​

Answer 1

vbg guidelines are online for the

Answer 2

Answer:

Sum of first n terms,

S

n

=

1−r

a(1−r

n

)

Sum of terms from (n+1)th to 2n th term is,

S

2n

−S

n

=

1−r

a(1−r

2n

)

−

1−r

a(1−r

n

)

=

1−r

a(r

n

−r

2n

)

Ratio,

=

1−r

a(r

n

−r

2n

)

1−r

a(1−r

n

)

=

r

n

−r

2n

1−r

n

=

r

n

(1−r

n

)

1−r

n

=

r

n

1

Hence proved.