Differention with repeat to x
cot^-1(x)
Answer: -2/(Squar root (1-9X^2)
i stuck...
Spoilers in white:
Using the chain rule: $\displaystyle {\color{white} \frac{d \, \cot y}{dx} = \frac{d \, \cot y}{dy} \cdot \frac{dy}{dx} = -\frac{1}{\sin^2 y} \frac{dy}{dx}.}$
Note that: $\displaystyle {\color{white} \cot y = x \Rightarrow \sin^2 y = \frac{1}{x^2 + 1}.}$