Chapter 2.2, Problem 44E

(a) By graphing the function $f(x)=\frac{\cos 2x-\cos x}{x^2}$ and zooming in toward the point where the graph crosses the $y$ -axis, estimate the value of $\underset{x\to 0}{\lim }f(x)$ .

(b) Check your answer in part (a) by evaluating $f(x)$ for values of $x$ that approach 0.