(d) $f(0) = \lim_{x \rightarrow 0}\frac{2x - \sin^{- 1}x}{2x + \tan^{- 1}x}$ $= \lim_{x \rightarrow 0}\frac{2 - \frac{\sin^{- 1}x}{x}}{2 + \frac{\tan^{- 1}x}{x}}$ $= \frac{2 - 1}{2 + 1} = \frac{1}{3}$
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Ph.D. in Physics with 19+ years of teaching experience.