#### Answer

The general formula to find the sum of the first n term of a Geometric sequence is given as: $ S_{n}=\dfrac{a_1(1-r^n)}{(1-r)}$

#### Work Step by Step

The general formula to find the sum of the first n term of a Geometric sequence is given as: $ S_{n}=\dfrac{a_1(1-r^n)}{(1-r)}$
In order to calculate the sum of the first n terms of a Geometric sequence we will multiply the first term $ a_1$ by the common difference between $1$ and the nth power of the common ratio; we then divide the result by the difference between $1$ and the common ration $ r $.