Find the sum of the following geometric series: `1,\ -a,\ a^2,-a^3, to\ n` terms `(a!=1)`

Explanation

Common Ratio `= r = −a/1 = -a `

∴ Sum of GP for n terms
`⇒ a = 1, r = - a, n = n`

∴ Substituting the above values in (1) we get

=`[-1((-a)^n-1)]/(a+1)`