Determine whether a sequence is a Geometric progression or not.
In mathematics, a **geometric progression**, also known as a **geometric sequence**, is a sequence of numbers where each term after the first is found by multiplying the previous one by a fixed, non-zero number called the common ratio. For example, the sequence 2, 6, 18, 54, ... is a geometric progression with common ratio 3. Similarly 10, 5, 2.5, 1.25, ... is a geometric sequence with common ratio 1/2.
Examples of a geometric sequence are powers $r^k$ of a fixed number r, such as $2^k$ and $3^k$. The general form of a geometric sequence is
$a,\ ar,\ ar^2,\ ar^3,\ ar^4,\ \ldots$
where r ≠ 0 is the common ratio and a is a scale factor, equal to the sequence's start value.