The statement is .

Consider left hand side statement .

Apply product rule of limits.

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Apply special trigonometric limits .

= Right hand side.

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The function .

Graph the function:

Observe the graph:

As tends to from the left hand side, then the limit approaches to .

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As tends to from the right hand side, then the limit approaches to .

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If the limit exists, then left hand limit is equal to right hand limit.

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The limit exists.

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Proved left hand side equal to right hand side.