Tex typo. $$\int arctan(x)$$ should be $$\frac{d}{dx} arctan(x)$$ in the first exercise of problem 8. See [calculusAndTaylorSeries/exercises/integralGuided.tex](https://github.com/mooculus/calculus/blob/master/calculusAndTaylorSeries/exercises/integralGuided.tex)
