I'm trying to solve this question but am finding it difficult to prove. I am using the negation of the Cauchy definition for sequences
$\exists >, \forall ∈\mathbb Z^+, \exists n,m>N, |a_n-a_m|\geq\epsilon$ for the integers $n\geq1, a_n=\sin(3n+1)$
Not sure how I need to manipulate the trig part of it to get my epsilon