Question 9***Evaluate \(\lim_{x\to0}\frac{x-\arctan x}{x^3}\), using \(\arctan x=x-\frac{x^3}{3}+\cdots\).
Question 18*****Diagnose the error: \(\frac{1-\cos x}{x}\) tends to \(\frac12\) because \(1-\cos x\) behaves like \(\frac{x^2}{2}\).
Question 20*****Why do \(\sin\theta\approx\theta\) and \(1-\cos\theta\approx\frac{\theta^2}{2}\) have different orders?