Question
Evaluate the following limit: $\lim\limits_{\text{x}\rightarrow0}\frac{\sin3\text{x}-\sin\text{x}}{\sin\text{x}}$

Answer

$\lim\limits_{\text{x}\rightarrow0}\frac{\sin3\text{x}-\sin\text{x}}{\sin\text{x}}$ $=\lim\limits_{\text{x}\rightarrow0}\Bigg(\frac{2\cos\big(\frac{3\text{x}+\text{x}}{2}\big)\sin\big(\frac{3\text{x}-\text{x}}{2}\big)}{\sin\text{x}}\Bigg)$ $=\lim\limits_{\text{x}\rightarrow0}\Big(\frac{2\cos2\text{x}\sin\text{x}}{\sin\text{x}}\Big)$ $=\lim\limits_{\text{x}\rightarrow0}(2\cos\text{x})$ $=2\lim\limits_{\text{x}\rightarrow0}\cos2\text{x}$
$=2\times\cos0$ $=2\times1=2$ $=2$

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