Home » Blog » Find the limit of the given function

Find the limit of the given function

Find the value of the following limit.

    \[ \lim_{x \to 0^+} \frac{x - \sin x}{(x \sin x)^{\frac{3}{2}}}. \]


First, since \lim_{x \to 0} \frac{\sin x}{x} = 1 we can multiply by this inside the limit without changing the value,

    \begin{align*}   \lim_{x \to 0^+} \frac{x - \sin x}{(x \sin x)^{\frac{3}{2}}} &= \lim_{x \to 0^+} \left( \frac{x - \sin x}{(x \sin x)^{\frac{3}{2}}} \cdot \left( \frac{\sin x}{x} \right)^{\frac{3}{2}} \right) \\[9pt]  &= \lim_{x \to 0^+} \frac{x - \sin x}{x^3}. \end{align*}

Now we can apply L’Hopital’s rule to compute the limit,

    \begin{align*}  \lim_{x \to 0^+} \frac{x - \sin x}{x^3} &= \frac{ 1 - \cos x}{3x^2} \\[9pt]  &= \lim_{x \to 0^+} \frac{ \sin x}{6x} \\[9pt]  &= \lim_{x \to 0^+} \frac{\cos x}{6} \\[9pt]  &= \frac{1}{6}. \end{align*}

Since this limit exists, the application of L’Hopital’s rule was justified.

Point out an error, ask a question, offer an alternative solution (to use Latex type [latexpage] at the top of your comment):