From the question it is given that,
The nth term of a G.P.
The sum of its n terms
Common ratio r =
We know that,
… [equation (i)]
Also we know that,
By cross multiplication we get,
… [equation (ii)]
Now, consider both the equation(i) and equation (ii)
By cross multiplication we get,
By simplification,
By comparing both LHS and RHS, we get,
Then,
Therefore, the value of a is
.