The series is geometric.

I will demonstrate how to find the sum of the first terms ofanygeometric sequence where is the first term of the sequence and is the ratio of the sequence.

The sum of the first terms, , is given by

(1)

Multiply both sides of the equation by .

(2)

Subtract equation 2 from equation 1.

Divide both sides of the equation by .

Now, it's a matter of recognizing geometric series and identifying and . What is and for the geometric series ?