9: After substituting the limit point into the given expression one gets

In the denominator, the sine part is negligible compared to x², so the denominator goes to infinity. This means that it would be possible to use l'Hospital's rule, but there is no point doing that. We know that differentiation does not make sines and cosines disappear.

A better approach is to use algebraic approach. One possibility is to replace sine and cosine with lower and upper bounds and see whether the Squeeze theorem succeeds.

Another option is to factor our dominant terms and try to work out the result.

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