Answer
$\{2,2.2,2.22,...\}$ is NOT an arithmetic sequence
Work Step by Step
In the given sequence, $\{
2,2.2,2.22,...
\},$ the differences of a term and its previous term are
\begin{align*}\require{cancel}
a_2-a_1&=
2.2-2
\\&=
0.2
,\\\\
a_3-a_2&=
2.22-2.2
\\&=
0.02
.\end{align*}
Since the differences of a term and its previous term are NOT the same, then $
\{2,2.2,2.22,...\}$ is NOT an arithmetic sequence
