Question

Find the sum of this GP : 1-(1/2)+(1/4)-(1/8)....... 9 terms

Answer 1

According to given sum,

a=1

common ratio (r)=(-1/2)/1=-1/2

sum of n terms of GP is

$s = a \times \frac{1 - {r}^{n} }{1 - r}$

sum of 9 terms is

$s = 1 \times \frac{1 - { (\frac{ - 1}{2} )}^{9} }{1 - ( \frac{ - 1}{2} )}$

$s = \frac{1 + \frac{1}{512} }{1 + \frac{1}{2} }$

$s = \frac{513}{512} \div \frac{3}{2}$

$s = \frac{171}{256}$

:-)Hope it helps u.

Answer 2

Q=find the sum of gp 1-1/2+1/4-1/8........9term

Answer

N= 9 terms

A= 1/2

A2=1/8

D=-3/8

Sn=9/2(2(1/2)+(9-1)-3/8)

=9/2(1+(8)-3/8)

=9/2(1-3)

=9/2(-2)

=-9 answer

I think this will help you