4: Since sine oscillates between −1 and 1, the whole sine part oscillates
between 1 and 3 and so the limit algebra cannot be used. The outcome of the
limit is determined by what comes out of the ratio by which this bounded(!)
oscillation is multiplied. Since "exponentials beat powers", it should go to
zero. This is a typical problem that can be solved using
l'Hospital's rule.
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