Answer
See below.
Work Step by Step
$a_3-a_2=\frac{7}{8}-\frac{15}{16}=\frac{14}{16}-\frac{15}{16}=-\frac{1}{16}= a_2-a_1=\frac{15}{16}-1=\frac{-1}{16} $, thus this is an arithmetic sequence.
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