Question
Evaluate: $\lim _{x \rightarrow 0} \frac{1-\cos 2 x}{x^2}$.

Answer

We have to find the value of 
$\begin{array}{l}\lim _{x \rightarrow 0} \frac{1-\cos 2 x}{x^2}=\lim _{x \rightarrow 0} \frac{2 \sin ^2 x}{x^2} \\ =2 \lim _{x \rightarrow 0}\left(\frac{\sin x}{x} \times \frac{\sin x}{x}\right)=2 \lim _{x \rightarrow 0} \frac{\sin x}{x} \times \lim _{x \rightarrow 0} \frac{\sin x}{x}=2(1)(1)=2\end{array}$

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